Archive-name: unix-faq/faq/contents Version: $Id: contents,v 2.7 1995/03/28 14:15:14 tmatimar Exp $
The following seven articles contain the answers to some Frequently Asked Questions often seen in comp.unix.questions and comp.unix.shell. Please don't ask these questions again, they've been answered plenty of times already - and please don't flame someone just because they may not have read this particular posting. Thank you.
This collection of documents is Copyright (c) 1994, Ted Timar, except Part 6, which is Copyright (c) 1994, Pierre Lewis and Ted Timar. All rights reserved. Permission to distribute the collection is hereby granted providing that distribution is electronic, no money is involved, reasonable attempts are made to use the latest version and all credits and this copyright notice are maintained. Other requests for distribution will be considered. All reasonable requests will be granted.
All information here has been contributed with good intentions, but none of it is guaranteed either by the contributors or myself to be accurate. The users of this information take all responsibility for any damage that may occur.
Many FAQs, including this one, are available on the archive site rtfm.mit.edu in the directory pub/usenet/news.answers. The name under which a FAQ is archived appears in the "Archive-Name:" line at the top of the article. This FAQ is archived as "unix-faq/faq/part[1-7]".
These articles are divided approximately as follows:
1.*) General questions.
2.*) Relatively basic questions, likely to be asked by beginners.
3.*) Intermediate questions.
4.*) Advanced questions, likely to be asked by people who thought
they already knew all of the answers.
5.*) Questions pertaining to the various shells, and the differences.
6.*) An overview of Unix variants.
7.*) An comparison of configuration management systems (RCS, SCCS).
The following questions are answered:
1.1) Who helped you put this list together?
1.2) When someone refers to 'rn(1)' or 'ctime(3)', what does
the number in parentheses mean?
1.3) What does {some strange unix command name} stand for?
1.4) How does the gateway between "comp.unix.questions" and the
"info-unix" mailing list work?
1.5) What are some useful Unix or C books?
1.6) What happened to the pronunciation list that used to be
part of this document?
2.1) How do I remove a file whose name begins with a "-" ?
2.2) How do I remove a file with funny characters in the filename ?
2.3) How do I get a recursive directory listing?
2.4) How do I get the current directory into my prompt?
2.5) How do I read characters from the terminal in a shell script?
2.6) How do I rename "*.foo" to "*.bar", or change file names
to lowercase?
2.7) Why do I get [some strange error message] when I
"rsh host command" ?
2.8) How do I {set an environment variable, change directory} inside a
program or shell script and have that change affect my
current shell?
2.9) How do I redirect stdout and stderr separately in csh?
2.10) How do I tell inside .cshrc if I'm a login shell?
2.11) How do I construct a shell glob-pattern that matches all files
except "." and ".." ?
2.12) How do I find the last argument in a Bourne shell script?
2.13) What's wrong with having '.' in your $PATH ?
2.14) How do I ring the terminal bell during a shell script?
2.15) Why can't I use "talk" to talk with my friend on machine X?
2.16) Why does calendar produce the wrong output?
3.1) How do I find the creation time of a file?
3.2) How do I use "rsh" without having the rsh hang around
until the remote command has completed?
3.3) How do I truncate a file?
3.4) Why doesn't find's "{}" symbol do what I want?
3.5) How do I set the permissions on a symbolic link?
3.6) How do I "undelete" a file?
3.7) How can a process detect if it's running in the background?
3.8) Why doesn't redirecting a loop work as intended? (Bourne shell)
3.9) How do I run 'passwd', 'ftp', 'telnet', 'tip' and other interactive
programs from a shell script or in the background?
3.10) How do I find the process ID of a program with a particular
name from inside a shell script or C program?
3.11) How do I check the exit status of a remote command
executed via "rsh" ?
3.12) Is it possible to pass shell variable settings into an awk program?
3.13) How do I get rid of zombie processes that persevere?
3.14) How do I get lines from a pipe as they are written instead of
only in larger blocks.
3.15) How do I get the date into a filename?
3.16) Why do some scripts start with #! ... ?
4.1) How do I read characters from a terminal without requiring the user
to hit RETURN?
4.2) How do I check to see if there are characters to be read without
actually reading?
4.3) How do I find the name of an open file?
4.4) How can an executing program determine its own pathname?
4.5) How do I use popen() to open a process for reading AND writing?
4.6) How do I sleep() in a C program for less than one second?
4.7) How can I get setuid shell scripts to work?
4.8) How can I find out which user or process has a file open or is using
a particular file system (so that I can unmount it?)
4.9) How do I keep track of people who are fingering me?
4.10) Is it possible to reconnect a process to a terminal after it has
been disconnected, e.g. after starting a program in the background
and logging out?
4.11) Is it possible to "spy" on a terminal, displaying the output
that's appearing on it on another terminal?
5.1) Can shells be classified into categories?
5.2) How do I "include" one shell script from within another
shell script?
5.3) Do all shells have aliases? Is there something else that
can be used?
5.4) How are shell variables assigned?
5.5) How can I tell if I am running an interactive shell?
5.6) What "dot" files do the various shells use?
5.7) I would like to know more about the differences between the
various shells. Is this information available some place?
6.1) Disclaimer and introduction.
6.2) A very brief look at Unix history.
6.3) Main Unix flavors.
6.4) Main Players and Unix Standards.
6.5) Identifying your Unix flavor.
6.6) Brief notes on some well-known (commercial/PD) Unices.
6.7) Real-time Unices.
6.8) Unix glossary.
6.9) Acknowledgements.
7.1) RCS vs SCCS: Introduction
7.2) RCS vs SCCS: How do the interfaces compare?
7.3) RCS vs SCCS: What's in a Revision File?
7.4) RCS vs SCCS: What are the keywords?
7.5) What's an RCS symbolic name?
7.6) RCS vs SCCS: How do they compare for performance?
7.7) RCS vs SCCS: Version Identification.
7.8) RCS vs SCCS: How do they handle with problems?
7.9) RCS vs SCCS: How do they interact with make(1)?
7.10) RCS vs SCCS: Conversion.
7.11) RCS vs SCCS: Support
7.12) RCS vs SCCS: Command Comparison
7.13) RCS vs SCCS: Acknowledgements
7.14) Can I get more information on configuration management systems?
If you're looking for the answer to, say, question 2.5, look in
part 2 and search for the regular expression "^2.5)".
While these are all legitimate questions, they seem to crop up in comp.unix.questions or comp.unix.shell on an annual basis, usually followed by plenty of replies (only some of which are correct) and then a period of griping about how the same questions keep coming up. You may also like to read the monthly article "Answers to Frequently Asked Questions" in the newsgroup "news.announce.newusers", which will tell you what "UNIX" stands for.
With the variety of Unix systems in the world, it's hard to guarantee that these answers will work everywhere. Read your local manual pages before trying anything suggested here. If you have suggestions or corrections for any of these answers, please send them to to tmatimar@isgtec.com.
-- Ted Timar - tmatimar@isgtec.com ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7
QUESTIONS AND ANSWERS
Subject: Who helped you put this list together?
Date: Thu Mar 18 17:16:55 EST 1993
This document was one of the first collections of Frequently Asked
Questions. It was originally compiled in July 1989.
I took over the maintenance of this list. Almost all of the work
(and the credit) for generating this compilation was done by
Steve Hayman.
We also owe a great deal of thanks to dozens of Usenet readers who
submitted questions, answers, corrections and suggestions for this
list. Special thanks go to Maarten Litmaath, Guy Harris and
Jonathan Kamens, who have all made many especially valuable
contributions.
Part 5 of this document (shells) was written almost entirely by
Matthew Wicks <wicks@dcdmjw.fnal.gov>.
Part 6 of this document (Unix flavours) was written almost entirely by
Pierre (P.) Lewis <lew@bnr.ca>.
Where possible the author of each question and the date it was last
updated is given at the top. Unfortunately, I only started this
practice recently, and much of the information is lost. I was also
negligent in keeping track of who provided updates to questions.
Sorry to those who have made valuable contributions, but did not
receive the credit and recognition that they legitimately deserve.
I make this document available in *roff format (ms and mm macro
packages). Andrew Cromarty has also converted it into Texinfo format.
Marty Leisner <leisner@sdsp.mc.xerox.com> cleaned up the Texinfo
version.
Major contributors to the this document who may or may not be
recognized elsewhere are:
Steve Hayman <shayman@Objectario.com>
Pierre Lewis <lew@bnr.ca>
Jonathon Kamens <jik@gza.com>
Tom Christiansen <tchrist@mox.perl.com>
Maarten Litmaath <maart@nat.vu.nl>
Guy Harris <guy@auspex.com>
The formatted versions are available for anonymous ftp from
ftp.wg.omron.co.jp under pub/unix-faq/docs .
------------------------------
Subject: When someone refers to 'rn(1)' ... the number in parentheses mean?
Date: Tue, 13 Dec 1994 16:37:26 -0500
the number in parentheses mean?
It looks like some sort of function call, but it isn't. These
numbers refer to the section of the "Unix manual" where the
appropriate documentation can be found. You could type
"man 3 ctime" to look up the manual page for "ctime" in section 3
of the manual.
The traditional manual sections are:
1 User-level commands
2 System calls
3 Library functions
4 Devices and device drivers
5 File formats
6 Games
7 Various miscellaneous stuff - macro packages etc.
8 System maintenance and operation commands
Some Unix versions use non-numeric section names. For instance,
Xenix uses "C" for commands and "S" for functions. Some newer
versions of Unix require "man -s# title" instead of "man # title".
Each section has an introduction, which you can read with "man #
intro" where # is the section number.
Sometimes the number is necessary to differentiate between a
command and a library routine or system call of the same name.
For instance, your system may have "time(1)", a manual page about
the 'time' command for timing programs, and also "time(3)", a
manual page about the 'time' subroutine for determining the
current time. You can use "man 1 time" or "man 3 time" to
specify which "time" man page you're interested in.
You'll often find other sections for local programs or even
subsections of the sections above - Ultrix has sections 3m, 3n,
3x and 3yp among others.
------------------------------
Subject: What does {some strange unix command name} stand for?
Date: Thu Mar 18 17:16:55 EST 1993
awk = "Aho Weinberger and Kernighan"
This language was named by its authors, Al Aho, Peter
Weinberger and Brian Kernighan.
grep = "Global Regular Expression Print"
grep comes from the ed command to print all lines matching a
certain pattern
g/re/p
where "re" is a "regular expression".
fgrep = "Fixed GREP".
fgrep searches for fixed strings only. The "f" does not stand
for "fast" - in fact, "fgrep foobar *.c" is usually slower than
"egrep foobar *.c" (Yes, this is kind of surprising. Try it.)
Fgrep still has its uses though, and may be useful when searching
a file for a larger number of strings than egrep can handle.
egrep = "Extended GREP"
egrep uses fancier regular expressions than grep. Many people
use egrep all the time, since it has some more sophisticated
internal algorithms than grep or fgrep, and is usually the
fastest of the three programs.
cat = "CATenate"
catenate is an obscure word meaning "to connect in a series",
which is what the "cat" command does to one or more files. Not
to be confused with C/A/T, the Computer Aided Typesetter.
gecos = "General Electric Comprehensive Operating Supervisor"
When GE's large systems division was sold to Honeywell,
Honeywell dropped the "E" from "GECOS".
Unix's password file has a "pw_gecos" field. The name is a
real holdover from the early days. Dennis Ritchie has reported:
"Sometimes we sent printer output or batch jobs
to the GCOS machine. The gcos field in the password file
was a place to stash the information for the $IDENT card.
Not elegant."
nroff = "New ROFF"
troff = "Typesetter new ROFF"
These are descendants of "roff", which was a re-implementation
of the Multics "runoff" program (a program that you'd use to
"run off" a good copy of a document).
tee = T
From plumbing terminology for a T-shaped pipe splitter.
bss = "Block Started by Symbol"
Dennis Ritchie says:
Actually the acronym (in the sense we took it up; it may
have other credible etymologies) is "Block Started by
Symbol." It was a pseudo-op in FAP (Fortran Assembly [-er?]
Program), an assembler for the IBM 704-709-7090-7094
machines. It defined its label and set aside space for a
given number of words. There was another pseudo-op, BES,
"Block Ended by Symbol" that did the same except that the
label was defined by the last assigned word + 1. (On these
machines Fortran arrays were stored backwards in storage
and were 1-origin.)
The usage is reasonably appropriate, because just as with
standard Unix loaders, the space assigned didn't have to be
punched literally into the object deck but was represented
by a count somewhere.
biff = "BIFF"
This command, which turns on asynchronous mail notification,
was actually named after a dog at Berkeley.
I can confirm the origin of biff, if you're interested.
Biff was Heidi Stettner's dog, back when Heidi (and I, and
Bill Joy) were all grad students at U.C. Berkeley and the
early versions of BSD were being developed. Biff was
popular among the residents of Evans Hall, and was known
for barking at the mailman, hence the name of the command.
Confirmation courtesy of Eric Cooper, Carnegie Mellon University
rc (as in ".cshrc" or "/etc/rc") = "RunCom"
"rc" derives from "runcom", from the MIT CTSS system, ca. 1965.
'There was a facility that would execute a bunch of
commands stored in a file; it was called "runcom" for "run
commands", and the file began to be called "a runcom."
"rc" in Unix is a fossil from that usage.'
Brian Kernighan & Dennis Ritchie, as told to Vicki Brown
"rc" is also the name of the shell from the new Plan 9
operating system.
Perl = "Practical Extraction and Report Language"
Perl = "Pathologically Eclectic Rubbish Lister"
The Perl language is Larry Wall's highly popular
freely-available completely portable text, process, and file
manipulation tool that bridges the gap between shell and C
programming (or between doing it on the command line and
pulling your hair out). For further information, see the
Usenet newsgroup comp.lang.perl.
Don Libes' book "Life with Unix" contains lots more of these
tidbits.
------------------------------
Subject: How does the gateway between "comp.unix.questions" ... work ?
Date: Thu Mar 18 17:16:55 EST 1993
"info-unix" mailing list work?
"info-unix" and "unix-wizards" are mailing list versions of
comp.unix.questions and comp.unix.wizards respectively.
There should be no difference in content between the
mailing list and the newsgroup.
To get on or off either of these lists, send mail to
info-unix-request@brl.mil or unix-wizards-request@brl.mil.
Be sure to use the '-Request'. Don't expect an immediate response.
Here are the gory details, courtesy of the list's maintainer,
Bob Reschly.
==== postings to info-UNIX and UNIX-wizards lists ====
Anything submitted to the list is posted; I do not moderate
incoming traffic -- BRL functions as a reflector. Postings
submitted by Internet subscribers should be addressed to the list
address (info-UNIX or UNIX- wizards); the '-request' addresses
are for correspondence with the list maintainer [me]. Postings
submitted by USENET readers should be addressed to the
appropriate news group (comp.unix.questions or
comp.unix.wizards).
For Internet subscribers, received traffic will be of two types;
individual messages, and digests. Traffic which comes to BRL
from the Internet and BITNET (via the BITNET-Internet gateway) is
immediately resent to all addressees on the mailing list.
Traffic originating on USENET is gathered up into digests which
are sent to all list members daily.
BITNET traffic is much like Internet traffic. The main
difference is that I maintain only one address for traffic
destined to all BITNET subscribers. That address points to a list
exploder which then sends copies to individual BITNET
subscribers. This way only one copy of a given message has to
cross the BITNET-Internet gateway in either direction.
USENET subscribers see only individual messages. All messages
originating on the Internet side are forwarded to our USENET
machine. They are then posted to the appropriate newsgroup.
Unfortunately, for gatewayed messages, the sender becomes
"news@brl-adm". This is currently an unavoidable side-effect of
the software which performs the gateway function.
As for readership, USENET has an extremely large readership - I
would guess several thousand hosts and tens of thousands of
readers. The master list maintained here at BRL runs about two
hundred fifty entries with roughly ten percent of those being
local redistribution lists. I don't have a good feel for the
size of the BITNET redistribution, but I would guess it is
roughly the same size and composition as the master list.
Traffic runs 150K to 400K bytes per list per week on average.
------------------------------
Subject: What are some useful Unix or C books?
Date: Thu Mar 18 17:16:55 EST 1993
Mitch Wright (mitch@cirrus.com) maintains a useful list of Unix
and C books, with descriptions and some mini-reviews. There are
currently 167 titles on his list.
You can obtain a copy of this list by anonymous ftp from
ftp.rahul.net (192.160.13.1), where it's "pub/mitch/YABL/yabl".
Send additions or suggestions to mitch@cirrus.com.
Samuel Ko (kko@sfu.ca) maintains another list of Unix books.
This list contains only recommended books, and is therefore
somewhat shorter. This list is also a classified list, with
books grouped into categories, which may be better if you are
looking for a specific type of book.
You can obtain a copy of this list by anonymous ftp from
rtfm.mit.edu, where it's "pub/usenet/news.answers/books/unix".
Send additions or suggestions to kko@sfu.ca.
If you can't use anonymous ftp, email the line "help" to
"ftpmail@decwrl.dec.com" for instructions on retrieving
things via email.
------------------------------
Subject: What happened to the pronunciation list ... ?
Date: Thu Mar 18 17:16:55 EST 1993
document?
From its inception in 1989, this FAQ document included a
comprehensive pronunciation list maintained by Maarten Litmaath
(thanks, Maarten!). It was originally created by Carl Paukstis
<carlp@frigg.isc-br.com>.
It has been retired, since it is not really relevant to the topic
of "Unix questions". You can still find it as part of the
widely-distributed "Jargon" file (maintained by Eric S. Raymond,
eric@snark.thyrsus.com) which seems like a much more appropriate
forum for the topic of "How do you pronounce /* ?"
If you'd like a copy, you can ftp one from ftp.wg.omron.co.jp
------------------------------
Subject: How do I remove a file whose name begins with a "-" ?
Date: Thu Mar 18 17:16:55 EST 1993
Figure out some way to name the file so that it doesn't begin
with a dash. The simplest answer is to use
rm ./-filename
(assuming "-filename" is in the current directory, of course.)
This method of avoiding the interpretation of the "-" works with
other commands too.
Many commands, particularly those that have been written to use
the "getopt(3)" argument parsing routine, accept a "--" argument
which means "this is the last option, anything after this is not
an option", so your version of rm might handle "rm -- -filename".
Some versions of rm that don't use getopt() treat a single "-"
in the same way, so you can also try "rm - -filename".
------------------------------
Subject: How do I remove a file with funny characters in the filename ?
Date: Thu Mar 18 17:16:55 EST 1993
If the 'funny character' is a '/', skip to the last part of this
answer. If the funny character is something else, such as a ' '
or control character or character with the 8th bit set, keep reading.
The classic answers are
rm -i some*pattern*that*matches*only*the*file*you*want
which asks you whether you want to remove each file matching
the indicated pattern; depending on your shell, this may not
work if the filename has a character with the 8th bit set (the
shell may strip that off);
and
rm -ri .
which asks you whether to remove each file in the directory.
Answer "y" to the problem file and "n" to everything else.
Unfortunately this doesn't work with many versions of rm. Also
unfortunately, this will walk through every subdirectory of ".",
so you might want to "chmod a-x" those directories temporarily
to make them unsearchable.
Always take a deep breath and think about what you're doing and
double check what you typed when you use rm's "-r" flag or a
wildcard on the command line;
and
find . -type f ... -ok rm '{}' \;
where "..." is a group of predicates that uniquely identify the
file. One possibility is to figure out the inode number of the
problem file (use "ls -i .") and then use
find . -inum 12345 -ok rm '{}' \;
or
find . -inum 12345 -ok mv '{}' new-file-name \;
"-ok" is a safety check - it will prompt you for confirmation of
the command it's about to execute. You can use "-exec" instead
to avoid the prompting, if you want to live dangerously, or if
you suspect that the filename may contain a funny character
sequence that will mess up your screen when printed.
What if the filename has a '/' in it?
These files really are special cases, and can only be created by
buggy kernel code (typically by implementations of NFS that don't
filter out illegal characters in file names from remote
machines.) The first thing to do is to try to understand exactly
why this problem is so strange.
Recall that Unix directories are simply pairs of filenames and
inode numbers. A directory essentially contains information
like this:
filename inode
file1 12345
file2.c 12349
file3 12347
Theoretically, '/' and '\0' are the only two characters that
cannot appear in a filename - '/' because it's used to separate
directories and files, and '\0' because it terminates a filename.
Unfortunately some implementations of NFS will blithely create
filenames with embedded slashes in response to requests from
remote machines. For instance, this could happen when someone on
a Mac or other non-Unix machine decides to create a remote NFS
file on your Unix machine with the date in the filename. Your
Unix directory then has this in it:
filename inode
91/02/07 12357
No amount of messing around with 'find' or 'rm' as described
above will delete this file, since those utilities and all other
Unix programs, are forced to interpret the '/' in the normal way.
Any ordinary program will eventually try to do
unlink("91/02/07"), which as far as the kernel is concerned means
"unlink the file 07 in the subdirectory 02 of directory 91", but
that's not what we have - we have a *FILE* named "91/02/07" in
the current directory. This is a subtle but crucial distinction.
What can you do in this case? The first thing to try is to
return to the Mac that created this crummy entry, and see if you
can convince it and your local NFS daemon to rename the file to
something without slashes.
If that doesn't work or isn't possible, you'll need help from
your system manager, who will have to try the one of the
following. Use "ls -i" to find the inode number of this bogus
file, then unmount the file system and use "clri" to clear the
inode, and "fsck" the file system with your fingers crossed.
This destroys the information in the file. If you want to keep
it, you can try:
create a new directory in the same parent directory as the one
containing the bad file name;
move everything you can (i.e. everything but the file with the
bad name) from the old directory to the new one;
do "ls -id" on the directory containing the file with the bad
name to get its inumber;
umount the file system;
"clri" the directory containing the file with the bad name;
"fsck" the file system.
Then, to find the file,
remount the file system;
rename the directory you created to have the name of the old
directory (since the old directory should have been blown away
by "fsck")
move the file out of "lost+found" into the directory with a
better name.
Alternatively, you can patch the directory the hard way by
crawling around in the raw file system. Use "fsdb", if you
have it.
------------------------------
Subject: How do I get a recursive directory listing?
Date: Thu Mar 18 17:16:55 EST 1993
One of the following may do what you want:
ls -R (not all versions of "ls" have -R)
find . -print (should work everywhere)
du -a . (shows you both the name and size)
If you're looking for a wildcard pattern that will match all ".c"
files in this directory and below, you won't find one, but you
can use
% some-command `find . -name '*.c' -print`
"find" is a powerful program. Learn about it.
------------------------------
Subject: How do I get the current directory into my prompt?
Date: Thu Mar 18 17:16:55 EST 1993
It depends which shell you are using. It's easy with some
shells, hard or impossible with others.
C Shell (csh):
Put this in your .cshrc - customize the prompt variable the
way you want.
alias setprompt 'set prompt="${cwd}% "'
setprompt # to set the initial prompt
alias cd 'chdir \!* && setprompt'
If you use pushd and popd, you'll also need
alias pushd 'pushd \!* && setprompt'
alias popd 'popd \!* && setprompt'
Some C shells don't keep a $cwd variable - you can use
`pwd` instead.
If you just want the last component of the current directory
in your prompt ("mail% " instead of "/usr/spool/mail% ")
you can use
alias setprompt 'set prompt="$cwd:t% "'
Some older csh's get the meaning of && and || reversed.
Try doing:
false && echo bug
If it prints "bug", you need to switch && and || (and get
a better version of csh.)
Bourne Shell (sh):
If you have a newer version of the Bourne Shell (SVR2 or newer)
you can use a shell function to make your own command, "xcd" say:
xcd() { cd $* ; PS1="`pwd` $ "; }
If you have an older Bourne shell, it's complicated but not
impossible. Here's one way. Add this to your .profile file:
LOGIN_SHELL=$$ export LOGIN_SHELL
CMDFILE=/tmp/cd.$$ export CMDFILE
# 16 is SIGURG, pick a signal that's not likely to be used
PROMPTSIG=16 export PROMPTSIG
trap '. $CMDFILE' $PROMPTSIG
and then put this executable script (without the indentation!),
let's call it "xcd", somewhere in your PATH
: xcd directory - change directory and set prompt
: by signalling the login shell to read a command file
cat >${CMDFILE?"not set"} <<EOF
cd $1
PS1="\`pwd\`$ "
EOF
kill -${PROMPTSIG?"not set"} ${LOGIN_SHELL?"not set"}
Now change directories with "xcd /some/dir".
Korn Shell (ksh):
Put this in your .profile file:
PS1='$PWD $ '
If you just want the last component of the directory, use
PS1='${PWD##*/} $ '
T C shell (tcsh)
Tcsh is a popular enhanced version of csh with some extra
builtin variables (and many other features):
%~ the current directory, using ~ for $HOME
%/ the full pathname of the current directory
%c or %. the trailing component of the current directory
so you can do
set prompt='%~ '
BASH (FSF's "Bourne Again SHell")
\w in $PS1 gives the full pathname of the current directory,
with ~ expansion for $HOME; \W gives the basename of
the current directory. So, in addition to the above sh and
ksh solutions, you could use
PS1='\w $ '
or
PS1='\W $ '
------------------------------
Subject: How do I read characters from the terminal in a shell script?
Date: Thu Mar 18 17:16:55 EST 1993
In sh, use read. It is most common to use a loop like
while read line
do
...
done
In csh, use $< like this:
while ( 1 )
set line = "$<"
if ( "$line" == "" ) break
...
end
Unfortunately csh has no way of distinguishing between a blank
line and an end-of-file.
If you're using sh and want to read a *single* character from the
terminal, you can try something like
echo -n "Enter a character: "
stty cbreak # or stty raw
readchar=`dd if=/dev/tty bs=1 count=1 2>/dev/null`
stty -cbreak
echo "Thank you for typing a $readchar ."
------------------------------
Subject: How do I rename "*.foo" to "*.bar", or change file names to lowercase?
Date: Thu Mar 18 17:16:55 EST 1993
Why doesn't "mv *.foo *.bar" work? Think about how the shell
expands wildcards. "*.foo" and "*.bar" are expanded before the
mv command ever sees the arguments. Depending on your shell,
this can fail in a couple of ways. CSH prints "No match."
because it can't match "*.bar". SH executes "mv a.foo b.foo
c.foo *.bar", which will only succeed if you happen to have a
single directory named "*.bar", which is very unlikely and almost
certainly not what you had in mind.
Depending on your shell, you can do it with a loop to "mv" each
file individually. If your system has "basename", you can use:
C Shell:
foreach f ( *.foo )
set base=`basename $f .foo`
mv $f $base.bar
end
Bourne Shell:
for f in *.foo; do
base=`basename $f .foo`
mv $f $base.bar
done
Some shells have their own variable substitution features, so
instead of using "basename", you can use simpler loops like:
C Shell:
foreach f ( *.foo )
mv $f $f:r.bar
end
Korn Shell:
for f in *.foo; do
mv $f ${f%foo}bar
done
If you don't have "basename" or want to do something like
renaming foo.* to bar.*, you can use something like "sed" to
strip apart the original file name in other ways, but the general
looping idea is the same. You can also convert file names into
"mv" commands with 'sed', and hand the commands off to "sh" for
execution. Try
ls -d *.foo | sed -e 's/.*/mv & &/' -e 's/foo$/bar/' | sh
A program by Vladimir Lanin called "mmv" that does this job
nicely was posted to comp.sources.unix (Volume 21, issues 87 and
88) in April 1990. It lets you use
mmv '*.foo' '=1.bar'
Shell loops like the above can also be used to translate file
names from upper to lower case or vice versa. You could use
something like this to rename uppercase files to lowercase:
C Shell:
foreach f ( * )
mv $f `echo $f | tr '[A-Z]' '[a-z]'`
end
Bourne Shell:
for f in *; do
mv $f `echo $f | tr '[A-Z]' '[a-z]'`
done
Korn Shell:
typeset -l l
for f in *; do
l="$f"
mv $f $l
done
If you wanted to be really thorough and handle files with `funny'
names (embedded blanks or whatever) you'd need to use
Bourne Shell:
for f in *; do
g=`expr "xxx$f" : 'xxx\(.*\)' | tr '[A-Z]' '[a-z]'`
mv "$f" "$g"
done
The `expr' command will always print the filename, even if it
equals `-n' or if it contains a System V escape sequence like `\c'.
Some versions of "tr" require the [ and ], some don't. It
happens to be harmless to include them in this particular
example; versions of tr that don't want the [] will conveniently
think they are supposed to translate '[' to '[' and ']' to ']'.
If you have the "perl" language installed, you may find this
rename script by Larry Wall very useful. It can be used to
accomplish a wide variety of filename changes.
#!/usr/bin/perl
#
# rename script examples from lwall:
# rename 's/\.orig$//' *.orig
# rename 'y/A-Z/a-z/ unless /^Make/' *
# rename '$_ .= ".bad"' *.f
# rename 'print "$_: "; s/foo/bar/ if <stdin> =~ /^y/i' *
$op = shift;
for (@ARGV) {
$was = $_;
eval $op;
die $@ if $@;
rename($was,$_) unless $was eq $_;
}
------------------------------
Subject: Why do I get [some strange error message] when I "rsh host command" ?
Date: Thu Mar 18 17:16:55 EST 1993
(We're talking about the remote shell program "rsh" or sometimes
"remsh" or "remote"; on some machines, there is a restricted shell
called "rsh", which is a different thing.)
If your remote account uses the C shell, the remote host will
fire up a C shell to execute 'command' for you, and that shell
will read your remote .cshrc file. Perhaps your .cshrc contains
a "stty", "biff" or some other command that isn't appropriate for
a non-interactive shell. The unexpected output or error message
from these commands can screw up your rsh in odd ways.
Here's an example. Suppose you have
stty erase ^H
biff y
in your .cshrc file. You'll get some odd messages like this.
% rsh some-machine date
stty: : Can't assign requested address
Where are you?
Tue Oct 1 09:24:45 EST 1991
You might also get similar errors when running certain "at" or
"cron" jobs that also read your .cshrc file.
Fortunately, the fix is simple. There are, quite possibly, a
whole *bunch* of operations in your ".cshrc" (e.g., "set
history=N") that are simply not worth doing except in interactive
shells. What you do is surround them in your ".cshrc" with:
if ( $?prompt ) then
operations....
endif
and, since in a non-interactive shell "prompt" won't be set, the
operations in question will only be done in interactive shells.
You may also wish to move some commands to your .login file; if
those commands only need to be done when a login session starts
up (checking for new mail, unread news and so on) it's better to
have them in the .login file.
------------------------------
Subject: How do I ... and have that change affect my current shell?
Date: Thu Mar 18 17:16:55 EST 1993
a program or shell script and have that change affect my
current shell?
In general, you can't, at least not without making special
arrangements. When a child process is created, it inherits a
copy of its parent's variables (and current directory). The
child can change these values all it wants but the changes won't
affect the parent shell, since the child is changing a copy of
the original data.
Some special arrangements are possible. Your child process could
write out the changed variables, if the parent was prepared to
read the output and interpret it as commands to set its own
variables.
Also, shells can arrange to run other shell scripts in the
context of the current shell, rather than in a child process, so
that changes will affect the original shell.
For instance, if you have a C shell script named "myscript":
cd /very/long/path
setenv PATH /something:/something-else
or the equivalent Bourne or Korn shell script
cd /very/long/path
PATH=/something:/something-else export PATH
and try to run "myscript" from your shell, your shell will fork
and run the shell script in a subprocess. The subprocess is also
running the shell; when it sees the "cd" command it changes *its*
current directory, and when it sees the "setenv" command it
changes *its* environment, but neither has any effect on the
current directory of the shell at which you're typing (your login
shell, let's say).
In order to get your login shell to execute the script (without
forking) you have to use the "." command (for the Bourne or Korn
shells) or the "source" command (for the C shell). I.e. you type
. myscript
to the Bourne or Korn shells, or
source myscript
to the C shell.
If all you are trying to do is change directory or set an
environment variable, it will probably be simpler to use a C
shell alias or Bourne/Korn shell function. See the "how do I get
the current directory into my prompt" section of this article for
some examples.
A much more detailed answer prepared by
xtm@telelogic.se (Thomas Michanek) can be found at
ftp.wg.omron.co.jp in /pub/unix-faq/docs/script-vs-env.
------------------------------
Subject: How do I redirect stdout and stderr separately in csh?
From: msb@sq.com (Mark Brader)
Date: Mon, 26 Oct 1992 20:15:00 -0500
In csh, you can redirect stdout with ">", or stdout and stderr
together with ">&" but there is no direct way to redirect stderr
only. The best you can do is
( command >stdout_file ) >&stderr_file
which runs "command" in a subshell; stdout is redirected inside
the subshell to stdout_file, and both stdout and stderr from the
subshell are redirected to stderr_file, but by this point stdout
has already been redirected so only stderr actually winds up in
stderr_file.
If what you want is to avoid redirecting stdout at all, let sh
do it for you.
sh -c 'command 2>stderr_file'
------------------------------
Subject: How do I tell inside .cshrc if I'm a login shell?
Date: Thu Mar 18 17:16:55 EST 1993
When people ask this, they usually mean either
How can I tell if it's an interactive shell? or
How can I tell if it's a top-level shell?
You could perhaps determine if your shell truly is a login shell
(i.e. is going to source ".login" after it is done with ".cshrc")
by fooling around with "ps" and "$$". Login shells generally
have names that begin with a '-'. If you're really interested in
the other two questions, here's one way you can organize your
.cshrc to find out.
if (! $?CSHLEVEL) then
#
# This is a "top-level" shell,
# perhaps a login shell, perhaps a shell started up by
# 'rsh machine some-command'
# This is where we should set PATH and anything else we
# want to apply to every one of our shells.
#
setenv CSHLEVEL 0
set home = ~username # just to be sure
source ~/.env # environment stuff we always want
else
#
# This shell is a child of one of our other shells so
# we don't need to set all the environment variables again.
#
set tmp = $CSHLEVEL
@ tmp++
setenv CSHLEVEL $tmp
endif
# Exit from .cshrc if not interactive, e.g. under rsh
if (! $?prompt) exit
# Here we could set the prompt or aliases that would be useful
# for interactive shells only.
source ~/.aliases
------------------------------
Subject: How do I construct a ... matches all files except "." and ".." ?
Date: Thu Mar 18 17:16:55 EST 1993
except "." and ".." ?
You'd think this would be easy.
* Matches all files that don't begin with a ".";
.* Matches all files that do begin with a ".", but
this includes the special entries "." and "..",
which often you don't want;
.[!.]* (Newer shells only; some shells use a "^" instead of
the "!"; POSIX shells must accept the "!", but may
accept a "^" as well; all portable applications shall
not use an unquoted "^" immediately following the "[")
Matches all files that begin with a "." and are
followed by a non-"."; unfortunately this will miss
"..foo";
.??* Matches files that begin with a "." and which are
at least 3 characters long. This neatly avoids
"." and "..", but also misses ".a" .
So to match all files except "." and ".." safely you have to use
3 patterns (if you don't have filenames like ".a" you can leave
out the first):
.[!.]* .??* *
Alternatively you could employ an external program or two and use
backquote substitution. This is pretty good:
`ls -a | sed -e '/^\.$/d' -e '/^\.\.$/d'`
(or `ls -A` in some Unix versions)
but even it will mess up on files with newlines, IFS characters
or wildcards in their names.
In ksh, you can use: .!(.|) *
------------------------------
Subject: How do I find the last argument in a Bourne shell script?
Date: Thu Mar 18 17:16:55 EST 1993
Answer by:
Martin Weitzel <@mikros.systemware.de:martin@mwtech.uucp>
Maarten Litmaath <maart@nat.vu.nl>
If you are sure the number of arguments is at most 9, you can use:
eval last=\${$#}
In POSIX-compatible shells it works for ANY number of arguments.
The following works always too:
for last
do
:
done
This can be generalized as follows:
for i
do
third_last=$second_last
second_last=$last
last=$i
done
Now suppose you want to REMOVE the last argument from the list,
or REVERSE the argument list, or ACCESS the N-th argument
directly, whatever N may be. Here is a basis of how to do it,
using only built-in shell constructs, without creating subprocesses:
t0= u0= rest='1 2 3 4 5 6 7 8 9' argv=
for h in '' $rest
do
for t in "$t0" $rest
do
for u in $u0 $rest
do
case $# in
0)
break 3
esac
eval argv$h$t$u=\$1
argv="$argv \"\$argv$h$t$u\"" # (1)
shift
done
u0=0
done
t0=0
done
# now restore the arguments
eval set x "$argv" # (2)
shift
This example works for the first 999 arguments. Enough?
Take a good look at the lines marked (1) and (2) and convince
yourself that the original arguments are restored indeed, no
matter what funny characters they contain!
To find the N-th argument now you can use this:
eval argN=\$argv$N
To reverse the arguments the line marked (1) must be changed to:
argv="\"\$argv$h$t$u\" $argv"
How to remove the last argument is left as an exercise.
If you allow subprocesses as well, possibly executing nonbuilt-in
commands, the `argvN' variables can be set up more easily:
N=1
for i
do
eval argv$N=\$i
N=`expr $N + 1`
done
To reverse the arguments there is still a simpler method, that
even does not create subprocesses. This approach can also be
taken if you want to delete e.g. the last argument, but in that
case you cannot refer directly to the N-th argument any more,
because the `argvN' variables are set up in reverse order:
argv=
for i
do
eval argv$#=\$i
argv="\"\$argv$#\" $argv"
shift
done
eval set x "$argv"
shift
------------------------------
Subject: What's wrong with having '.' in your $PATH ?
Date: Thu Mar 18 17:16:55 EST 1993
A bit of background: the PATH environment variable is a list of
directories separated by colons. When you type a command name
without giving an explicit path (e.g. you type "ls", rather than
"/bin/ls") your shell searches each directory in the PATH list in
order, looking for an executable file by that name, and the shell
will run the first matching program it finds.
One of the directories in the PATH list can be the current
directory "." . It is also permissible to use an empty directory
name in the PATH list to indicate the current directory. Both of
these are equivalent
for csh users:
setenv PATH :/usr/ucb:/bin:/usr/bin
setenv PATH .:/usr/ucb:/bin:/usr/bin
for sh or ksh users
PATH=:/usr/ucb:/bin:/usr/bin export PATH
PATH=.:/usr/ucb:/bin:/usr/bin export PATH
Having "." somewhere in the PATH is convenient - you can type
"a.out" instead of "./a.out" to run programs in the current
directory. But there's a catch.
Consider what happens in the case where "." is the first entry
in the PATH. Suppose your current directory is a publically-
writable one, such as "/tmp". If there just happens to be a
program named "/tmp/ls" left there by some other user, and you
type "ls" (intending, of course, to run the normal "/bin/ls"
program), your shell will instead run "./ls", the other user's
program. Needless to say, the results of running an unknown
program like this might surprise you.
It's slightly better to have "." at the end of the PATH:
setenv PATH /usr/ucb:/bin:/usr/bin:.
Now if you're in /tmp and you type "ls", the shell will
search /usr/ucb, /bin and /usr/bin for a program named
"ls" before it gets around to looking in ".", and there
is less risk of inadvertently running some other user's
"ls" program. This isn't 100% secure though - if you're
a clumsy typist and some day type "sl -l" instead of "ls -l",
you run the risk of running "./sl", if there is one.
Some "clever" programmer could anticipate common typing
mistakes and leave programs by those names scattered
throughout public directories. Beware.
Many seasoned Unix users get by just fine without having
"." in the PATH at all:
setenv PATH /usr/ucb:/bin:/usr/bin
If you do this, you'll need to type "./program" instead
of "program" to run programs in the current directory, but
the increase in security is probably worth it.
------------------------------
Subject: How do I ring the terminal bell during a shell script?
From: uwe@mpi-sb.mpg.de (Uwe Waldmann)
Date: Fri, 30 Apr 93 16:33:00 +0200
The answer depends on your Unix version (or rather on the kind of
"echo" program that is available on your machine).
A BSD-like "echo" uses the "-n" option for suppressing the final
newline and does not understand the octal \nnn notation. Thus
the command is
echo -n '^G'
where ^G means a _literal_ BEL-character (you can produce this in
emacs using "Ctrl-Q Ctrl-G" and in vi using "Ctrl-V Ctrl-G").
A SysV-like "echo" understands the \nnn notation and uses \c to
suppress the final newline, so the answer is:
echo '\007\c'
------------------------------
Subject: Why can't I use "talk" to talk with my friend on machine X?
From: tmatimar@isgtec.com (Ted Timar)
Date: Thu Mar 18 17:16:55 EST 1993
Unix has three common "talk" programs, none of which can talk with
any of the others. The "old" talk accounts for the first two types.
This version (often called otalk) did not take "endian" order into
account when talking to other machines. As a consequence, the Vax
version of otalk cannot talk with the Sun version of otalk.
These versions of talk use port 517.
Around 1987, most vendors (except Sun, who took 6 years longer than
any of their competitors) standardized on a new talk (often called
ntalk) which knows about network byte order. This talk works between
all machines that have it. This version of talk uses port 518.
There are now a few talk programs that speak both ntalk and one
version of otalk. The most common of these is called "ytalk".
------------------------------
Subject: Why does calendar produce the wrong output?
From: tmatimar@isgtec.com (Ted Timar)
Date: Thu Sep 8 09:45:46 EDT 1994
Frequently, people find that the output for the Unix calendar
program, 'cal' produces output that they do not expect.
The calendar for September 1752 is very odd:
September 1752
S M Tu W Th F S
1 2 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
This is the month in which the US (the entire British Empire actually)
switched from the Julian to the Gregorian calendar.
The other common problem people have with the calendar program is
that they pass it arguments like 'cal 9 94'. This gives the calendar
for September of AD 94, NOT 1994.
------------------------------
Subject: How do I find the creation time of a file?
Date: Thu Mar 18 17:16:55 EST 1993
You can't - it isn't stored anywhere. Files have a last-modified
time (shown by "ls -l"), a last-accessed time (shown by "ls -lu")
and an inode change time (shown by "ls -lc"). The latter is often
referred to as the "creation time" - even in some man pages -
but that's wrong; it's also set by such operations as mv, ln,
chmod, chown and chgrp.
The man page for "stat(2)" discusses this.
------------------------------
Subject: How do I use "rsh" without having the rsh hang around ... ?
Date: Thu Mar 18 17:16:55 EST 1993
remote command has completed?
(See note in question 2.7 about what "rsh" we're talking about.)
The obvious answers fail:
rsh machine command &
or rsh machine 'command &'
For instance, try doing rsh machine 'sleep 60 &' and you'll see
that the 'rsh' won't exit right away. It will wait 60 seconds
until the remote 'sleep' command finishes, even though that
command was started in the background on the remote machine. So
how do you get the 'rsh' to exit immediately after the 'sleep' is
started?
The solution - if you use csh on the remote machine:
rsh machine -n 'command >&/dev/null </dev/null &'
If you use sh on the remote machine:
rsh machine -n 'command >/dev/null 2>&1 </dev/null &'
Why? "-n" attaches rsh's stdin to /dev/null so you could run the
complete rsh command in the background on the LOCAL machine.
Thus "-n" is equivalent to another specific "< /dev/null".
Furthermore, the input/output redirections on the REMOTE machine
(inside the single quotes) ensure that rsh thinks the session can
be terminated (there's no data flow any more.)
Note: The file that you redirect to/from on the remote machine
doesn't have to be /dev/null; any ordinary file will do.
In many cases, various parts of these complicated commands
aren't necessary.
------------------------------
Subject: How do I truncate a file?
Date: Mon, 27 Mar 1995 18:09:10 -0500
The BSD function ftruncate() sets the length of a file.
(But not all versions behave identically.) Other Unix variants
all seem to support some version of truncation as well.
For systems which support the ftruncate function, there are
three known behaviours:
BSD 4.2 - Ultrix, SGI, LynxOS
- truncation doesn't grow file
- truncation doesn't move file pointer
BSD 4.3 - SunOS, Solaris, OSF/1, HP/UX, Amiga
- truncation can grow file
- truncation doesn't move file pointer
Cray - UniCOS 7, UniCOS 8
- truncation doesn't grow file
- truncation changes file pointer
Other systems come in four varieties:
F_CHSIZE - Only SCO
- some systems define F_CHSIZE but don't support it
- behaves like BSD 4.3
F_FREESP - Only Interative Unix
- some systems (eg. Interactive Unix) define F_FREESP but
don't support it
- behaves like BSD 4.3
chsize() - QNX and SCO
- some systems (eg. Interactive Unix) have chsize() but
don't support it
- behaves like BSD 4.3
nothing - no known systems
- there will be systems that don't support truncate at all
Moderator's Note: I grabbed the functions below a few years back.
I can no longer identify the original author.
S. Spencer Sun <spencer@ncd.com> has also
contributed a version for F_FREESP.
functions for each non-native ftruncate follow
/* ftruncate emulations that work on some System V's.
This file is in the public domain. */
#include
#include
#ifdef F_CHSIZE
int
ftruncate (fd, length)
int fd;
off_t length;
{
return fcntl (fd, F_CHSIZE, length);
}
#else
#ifdef F_FREESP
/* The following function was written by
kucharsk@Solbourne.com (William Kucharski) */
#include
#include
#include
int
ftruncate (fd, length)
int fd;
off_t length;
{
struct flock fl;
struct stat filebuf;
if (fstat (fd, &filebuf) < 0)
return -1;
if (filebuf.st_size < length)
{
/* Extend file length. */
if (lseek (fd, (length - 1), SEEK_SET) < 0)
return -1;
/* Write a "0" byte. */
if (write (fd, "", 1) != 1)
return -1;
}
else
{
/* Truncate length. */
fl.l_whence = 0;
fl.l_len = 0;
fl.l_start = length;
fl.l_type = F_WRLCK; /* Write lock on file space. */
/* This relies on the UNDOCUMENTED F_FREESP argument to
fcntl, which truncates the file so that it ends at the
position indicated by fl.l_start.
Will minor miracles never cease? */
if (fcntl (fd, F_FREESP, &fl) < 0)
return -1;
}
return 0;
}
#else
int
ftruncate (fd, length)
int fd;
off_t length;
{
return chsize (fd, length);
}
#endif
#endif
------------------------------
Subject: Why doesn't find's "{}" symbol do what I want?
Date: Thu Mar 18 17:16:55 EST 1993
"find" has a -exec option that will execute a particular command
on all the selected files. Find will replace any "{}" it sees
with the name of the file currently under consideration.
So, some day you might try to use "find" to run a command on
every file, one directory at a time. You might try this:
find /path -type d -exec command {}/\* \;
hoping that find will execute, in turn
command directory1/*
command directory2/*
...
Unfortunately, find only expands the "{}" token when it appears
by itself. Find will leave anything else like "{}/*" alone, so
instead of doing what you want, it will do
command {}/*
command {}/*
...
once for each directory. This might be a bug, it might be a
feature, but we're stuck with the current behaviour.
So how do you get around this? One way would be to write a
trivial little shell script, let's say "./doit", that consists of
command "$1"/*
You could then use
find /path -type d -exec ./doit {} \;
Or if you want to avoid the "./doit" shell script, you can use
find /path -type d -exec sh -c 'command $0/*' {} \;
(This works because within the 'command' of "sh -c 'command' A B C ...",
$0 expands to A, $1 to B, and so on.)
or you can use the construct-a-command-with-sed trick
find /path -type d -print | sed 's:.*:command &/*:' | sh
If all you're trying to do is cut down on the number of times
that "command" is executed, you should see if your system has the
"xargs" command. Xargs reads arguments one line at a time from
the standard input and assembles as many of them as will fit into
one command line. You could use
find /path -print | xargs command
which would result in one or more executions of
command file1 file2 file3 file4 dir1/file1 dir1/file2
Unfortunately this is not a perfectly robust or secure solution.
Xargs expects its input lines to be terminated with newlines, so
it will be confused by files with odd characters such as newlines
in their names.
------------------------------
Subject: How do I set the permissions on a symbolic link?
Date: Thu Mar 18 17:16:55 EST 1993
Permissions on a symbolic link don't really mean anything. The
only permissions that count are the permissions on the file that
the link points to.
------------------------------
Subject: How do I "undelete" a file?
Date: Thu Mar 18 17:16:55 EST 1993
Someday, you are going to accidentally type something like
"rm * .foo", and find you just deleted "*" instead of "*.foo".
Consider it a rite of passage.
Of course, any decent systems administrator should be doing
regular backups. Check with your sysadmin to see if a recent
backup copy of your file is available. But if it isn't, read
on.
For all intents and purposes, when you delete a file with "rm" it
is gone. Once you "rm" a file, the system totally forgets which
blocks scattered around the disk were part of your file. Even
worse, the blocks from the file you just deleted are going to be
the first ones taken and scribbled upon when the system needs
more disk space. However, never say never. It is theoretically
possible *if* you shut down the system immediately after the "rm"
to recover portions of the data. However, you had better have a
very wizardly type person at hand with hours or days to spare to
get it all back.
Your first reaction when you "rm" a file by mistake is why not
make a shell alias or procedure which changes "rm" to move files
into a trash bin rather than delete them? That way you can
recover them if you make a mistake, and periodically clean out
your trash bin. Two points: first, this is generally accepted
as a *bad* idea. You will become dependent upon this behaviour
of "rm", and you will find yourself someday on a normal system
where "rm" is really "rm", and you will get yourself in trouble.
Second, you will eventually find that the hassle of dealing with
the disk space and time involved in maintaining the trash bin, it
might be easier just to be a bit more careful with "rm". For
starters, you should look up the "-i" option to "rm" in your
manual.
If you are still undaunted, then here is a possible simple
answer. You can create yourself a "can" command which moves
files into a trashcan directory. In csh(1) you can place the
following commands in the ".login" file in your home directory:
alias can 'mv \!* ~/.trashcan' # junk file(s) to trashcan
alias mtcan 'rm -f ~/.trashcan/*' # irretrievably empty trash
if ( ! -d ~/.trashcan ) mkdir ~/.trashcan # ensure trashcan exists
You might also want to put a:
rm -f ~/.trashcan/*
in the ".logout" file in your home directory to automatically
empty the trash when you log out. (sh and ksh versions are left
as an exercise for the reader.)
MIT's Project Athena has produced a comprehensive
delete/undelete/expunge/purge package, which can serve as a
complete replacement for rm which allows file recovery. This
package was posted to comp.sources.misc (volume 17, issue
023-026)
------------------------------
Subject: How can a process detect if it's running in the background?
Date: Thu Mar 18 17:16:55 EST 1993
First of all: do you want to know if you're running in the
background, or if you're running interactively? If you're
deciding whether or not you should print prompts and the like,
that's probably a better criterion. Check if standard input
is a terminal:
sh: if [ -t 0 ]; then ... fi
C: if(isatty(0)) { ... }
In general, you can't tell if you're running in the background.
The fundamental problem is that different shells and different
versions of UNIX have different notions of what "foreground" and
"background" mean - and on the most common type of system with a
better-defined notion of what they mean, programs can be moved
arbitrarily between foreground and background!
UNIX systems without job control typically put a process into the
background by ignoring SIGINT and SIGQUIT and redirecting the
standard input to "/dev/null"; this is done by the shell.
Shells that support job control, on UNIX systems that support job
control, put a process into the background by giving it a process
group ID different from the process group to which the terminal
belongs. They move it back into the foreground by setting the
terminal's process group ID to that of the process. Shells that
do *not* support job control, on UNIX systems that support job
control, typically do what shells do on systems that don't
support job control.
------------------------------
Subject: Why doesn't redirecting a loop work as intended? (Bourne shell)
Date: Thu Mar 18 17:16:55 EST 1993
Take the following example:
foo=bar
while read line
do
# do something with $line
foo=bletch
done < /etc/passwd
echo "foo is now: $foo"
Despite the assignment ``foo=bletch'' this will print
``foo is now: bar'' in many implementations of the Bourne shell.
Why? Because of the following, often undocumented, feature of
historic Bourne shells: redirecting a control structure (such as
a loop, or an ``if'' statement) causes a subshell to be created,
in which the structure is executed; variables set in that
subshell (like the ``foo=bletch'' assignment) don't affect the
current shell, of course.
The POSIX 1003.2 Shell and Tools Interface standardization
committee forbids the behaviour described above, i.e. in P1003.2
conformant Bourne shells the example will print ``foo is now:
bletch''.
In historic (and P1003.2 conformant) implementations you can use
the following `trick' to get around the redirection problem:
foo=bar
# make file descriptor 9 a duplicate of file descriptor 0 (stdin);
# then connect stdin to /etc/passwd; the original stdin is now
# `remembered' in file descriptor 9; see dup(2) and sh(1)
exec 9<&0 < /etc/passwd
while read line
do
# do something with $line
foo=bletch
done
# make stdin a duplicate of file descriptor 9, i.e. reconnect
# it to the original stdin; then close file descriptor 9
exec 0<&9 9<&-
echo "foo is now: $foo"
This should always print ``foo is now: bletch''.
Right, take the next example:
foo=bar
echo bletch | read foo
echo "foo is now: $foo"
This will print ``foo is now: bar'' in many implementations,
``foo is now: bletch'' in some others. Why? Generally each part
of a pipeline is run in a different subshell; in some
implementations though, the last command in the pipeline is made
an exception: if it is a builtin command like ``read'', the
current shell will execute it, else another subshell is created.
POSIX 1003.2 allows both behaviours so portable scripts cannot
depend on any of them.
------------------------------
Subject: How do I run ... interactive programs from a shell script ... ?
Date: Thu Mar 18 17:16:55 EST 1993
programs from a shell script or in the background?
These programs expect a terminal interface. Shells makes no
special provisions to provide one. Hence, such programs cannot
be automated in shell scripts.
The 'expect' program provides a programmable terminal interface
for automating interaction with such programs. The following
expect script is an example of a non-interactive version of
passwd(1).
# username is passed as 1st arg, password as 2nd
set password [index $argv 2]
spawn passwd [index $argv 1]
expect "*password:"
send "$password\r"
expect "*password:"
send "$password\r"
expect eof
expect can partially automate interaction which is especially
useful for telnet, rlogin, debuggers or other programs that have
no built-in command language. The distribution provides an
example script to rerun rogue until a good starting configuration
appears. Then, control is given back to the user to enjoy the game.
Fortunately some programs have been written to manage the
connection to a pseudo-tty so that you can run these sorts of
programs in a script.
To get expect, email "send pub/expect/expect.shar.Z" to
library@cme.nist.gov or anonymous ftp same from
ftp.cme.nist.gov.
Another solution is provided by the pty 4.0 program, which runs a
program under a pseudo-tty session and was posted to
comp.sources.unix, volume 25. A pty-based solution using named
pipes to do the same as the above might look like this:
#!/bin/sh
/etc/mknod out.$$ p; exec 2>&1
( exec 4<out.$$; rm -f out.$$
<&4 waitfor 'password:'
echo "$2"
<&4 waitfor 'password:'
echo "$2"
<&4 cat >/dev/null
) | ( pty passwd "$1" >out.$$ )
Here, 'waitfor' is a simple C program that searches for
its argument in the input, character by character.
A simpler pty solution (which has the drawback of not
synchronizing properly with the passwd program) is
#!/bin/sh
( sleep 5; echo "$2"; sleep 5; echo "$2") | pty passwd "$1"
------------------------------
Subject: How do I find the process ID of a program with a particular name ... ?
Date: Thu Mar 18 17:16:55 EST 1993
from inside a shell script or C program?
In a shell script:
There is no utility specifically designed to map between program
names and process IDs. Furthermore, such mappings are often
unreliable, since it's possible for more than one process to have
the same name, and since it's possible for a process to change
its name once it starts running. However, a pipeline like this
can often be used to get a list of processes (owned by you) with
a particular name:
ps ux | awk '/name/ && !/awk/ {print $2}'
You replace "name" with the name of the process for which you are
searching.
The general idea is to parse the output of ps, using awk or grep
or other utilities, to search for the lines with the specified
name on them, and print the PID's for those lines. Note that the
"!/awk/" above prevents the awk process for being listed.
You may have to change the arguments to ps, depending on what
kind of Unix you are using.
In a C program:
Just as there is no utility specifically designed to map between
program names and process IDs, there are no (portable) C library
functions to do it either.
However, some vendors provide functions for reading Kernel
memory; for example, Sun provides the "kvm_" functions, and Data
General provides the "dg_" functions. It may be possible for any
user to use these, or they may only be useable by the super-user
(or a user in group "kmem") if read-access to kernel memory on
your system is restricted. Furthermore, these functions are
often not documented or documented badly, and might change from
release to release.
Some vendors provide a "/proc" filesystem, which appears as a
directory with a bunch of filenames in it. Each filename is a
number, corresponding to a process ID, and you can open the file
and read it to get information about the process. Once again,
access to this may be restricted, and the interface to it may
change from system to system.
If you can't use vendor-specific library functions, and you
don't have /proc, and you still want to do this completely
in C, you
are going to have to do the rummaging through kernel memory
yourself. For a good example of how to do this on many systems,
see the sources to "ofiles", available in the comp.sources.unix
archives. (A package named "kstuff" to help with kernel
rummaging was posted to alt.sources in May 1991 and is also
available via anonymous ftp as
usenet/alt.sources/articles/{329{6,7,8,9},330{0,1}}.Z from
wuarchive.wustl.edu.)
------------------------------
Subject: How do I check the exit status of a remote command executed via "rsh"?
Date: Thu Mar 18 17:16:55 EST 1993
executed via "rsh" ?
This doesn't work:
rsh some-machine some-crummy-command || echo "Command failed"
The exit status of 'rsh' is 0 (success) if the rsh program
itself completed successfully, which probably isn't what
you wanted.
If you want to check on the exit status of the remote program,
you can try using Maarten Litmaath's 'ersh' script, which was
posted to alt.sources in October 1994. ersh is a shell script
that calls rsh, arranges for the remote machine to echo the
status of the command after it completes, and exits with that
status.
------------------------------
Subject: Is it possible to pass shell variable settings into an awk program?
Date: Thu Mar 18 17:16:55 EST 1993
There are two different ways to do this. The first involves
simply expanding the variable where it is needed in the program.
For example, to get a list of all ttys you're using:
who | awk '/^'"$USER"'/ { print $2 }' (1)
Single quotes are usually used to enclose awk programs because
the character '$' is often used in them, and '$' will be
interpreted by the shell if enclosed inside double quotes, but
not if enclosed inside single quotes. In this case, we *want*
the '$' in "$USER" to be interpreted by the shell, so we close
the single quotes and then put the "$USER" inside double quotes.
Note that there are no spaces in any of that, so the shell will
see it all as one argument. Note, further, that the double
quotes probably aren't necessary in this particular case (i.e. we
could have done
who | awk '/^'$USER'/ { print $2 }' (2)
), but they should be included nevertheless because they are
necessary when the shell variable in question contains special
characters or spaces.
The second way to pass variable settings into awk is to use an
often undocumented feature of awk which allows variable settings
to be specified as "fake file names" on the command line. For
example:
who | awk '$1 == user { print $2 }' user="$USER" - (3)
Variable settings take effect when they are encountered on the
command line, so, for example, you could instruct awk on how to
behave for different files using this technique. For example:
awk '{ program that depends on s }' s=1 file1 s=0 file2 (4)
Note that some versions of awk will cause variable settings
encountered before any real filenames to take effect before the
BEGIN block is executed, but some won't so neither way should be
relied upon.
Note, further, that when you specify a variable setting, awk
won't automatically read from stdin if no real files are
specified, so you need to add a "-" argument to the end of your
command, as I did at (3) above.
A third option is to use a newer version of awk (nawk), which allows
direct access to environment vairables. Eg.
nawk 'END { print "Your path variable is " ENVIRON["PATH"] }' /dev/null
------------------------------
Subject: How do I get rid of zombie processes that persevere?
From: jik@rtfm.MIT.Edu (Jonathan I. Kamens)
From: casper@fwi.uva.nl (Casper Dik)
Date: Thu, 09 Sep 93 16:39:58 +0200
Unfortunately, it's impossible to generalize how the death of
child processes should behave, because the exact mechanism varies
over the various flavors of Unix.
First of all, by default, you have to do a wait() for child
processes under ALL flavors of Unix. That is, there is no flavor
of Unix that I know of that will automatically flush child
processes that exit, even if you don't do anything to tell it to
do so.
Second, under some SysV-derived systems, if you do
"signal(SIGCHLD, SIG_IGN)" (well, actually, it may be SIGCLD
instead of SIGCHLD, but most of the newer SysV systems have
"#define SIGCHLD SIGCLD" in the header files), then child
processes will be cleaned up automatically, with no further
effort in your part. The best way to find out if it works at
your site is to try it, although if you are trying to write
portable code, it's a bad idea to rely on this in any case.
Unfortunately, POSIX doesn't allow you to do this; the behavior
of setting the SIGCHLD to SIG_IGN under POSIX is undefined, so
you can't do it if your program is supposed to be
POSIX-compliant.
So, what's the POSIX way? As mentioned earlier, you must
install a signal handler and wait. Under POSIX signal handlers
are installed with sigaction. Since you are not interested in
``stopped'' children, only in terminated children, add SA_NOCLDSTOP
to sa_flags. Waiting without blocking is done with waitpid().
The first argument to waitpid should be -1 (wait for any pid),
the third should be WNOHANG. This is the most portable way
and is likely to become more portable in future.
If your systems doesn't support POSIX, there's a number of ways.
The easiest way is signal(SIGCHLD, SIG_IGN), if it works.
If SIG_IGN cannot be used to force automatic clean-up, then you've
got to write a signal handler to do it. It isn't easy at all to
write a signal handler that does things right on all flavors of
Unix, because of the following inconsistencies:
On some flavors of Unix, the SIGCHLD signal handler is called if
one *or more* children have died. This means that if your signal
handler only does one wait() call, then it won't clean up all of
the children. Fortunately, I believe that all Unix flavors for
which this is the case have available to the programmer the
wait3() or waitpid() call, which allows the WNOHANG option to
check whether or not there are any children waiting to be cleaned
up. Therefore, on any system that has wait3()/waitpid(), your
signal handler should call wait3()/waitpid() over and over again
with the WNOHANG option until there are no children left to clean
up. Waitpid() is the preferred interface, as it is in POSIX.
On SysV-derived systems, SIGCHLD signals are regenerated if there
are child processes still waiting to be cleaned up after you exit
the SIGCHLD signal handler. Therefore, it's safe on most SysV
systems to assume when the signal handler gets called that you
only have to clean up one signal, and assume that the handler
will get called again if there are more to clean up after it
exits.
On older systems, there is no way to prevent signal handlers
from being automatically reset to SIG_DFL when the signal
handler gets called. On such systems, you have to put
"signal(SIGCHILD, catcher_func)" (where "catcher_func" is the
name of the handler function) as the last thing in the signal
handler, so that it gets reset.
Fortunately, newer implementations allow signal handlers to be
installed without being reset to SIG_DFL when the handler
function is called. To get around this problem, on systems that
do not have wait3()/waitpid() but do have SIGCLD, you need to
reset the signal handler with a call to signal() after doing at
least one wait() within the handler, each time it is called. For
backward compatibility reasons, System V will keep the old
semantics (reset handler on call) of signal(). Signal handlers
that stick can be installed with sigaction() or sigset().
The summary of all this is that on systems that have waitpid()
(POSIX) or wait3(), you should use that and your signal handler
should loop, and on systems that don't, you should have one call
to wait() per invocation of the signal handler.
One more thing -- if you don't want to go through all of this
trouble, there is a portable way to avoid this problem, although
it is somewhat less efficient. Your parent process should fork,
and then wait right there and then for the child process to
terminate. The child process then forks again, giving you a
child and a grandchild. The child exits immediately (and hence
the parent waiting for it notices its death and continues to
work), and the grandchild does whatever the child was originally
supposed to. Since its parent died, it is inherited by init,
which will do whatever waiting is needed. This method is
inefficient because it requires an extra fork, but is pretty much
completely portable.
------------------------------
Subject: How do I get lines from a pipe ... instead of only in larger blocks?
From: jik@rtfm.MIT.Edu (Jonathan I. Kamens)
Date: Sun, 16 Feb 92 20:59:28 -0500
larger blocks?
The stdio library does buffering differently depending on whether
it thinks it's running on a tty. If it thinks it's on a tty, it
does buffering on a per-line basis; if not, it uses a larger
buffer than one line.
If you have the source code to the client whose buffering you
want to disable, you can use setbuf() or setvbuf() to change the
buffering.
If not, the best you can do is try to convince the program that
it's running on a tty by running it under a pty, e.g. by using
the "pty" program mentioned in question 3.9.
------------------------------
Subject: How do I get the date into a filename?
From: melodie neal <melodie@comtech.ct.oz.au>
Date: Fri, 7 Oct 1994 09:27:33 -0400
This isn't hard, but it is a bit cryptic at first sight. Let's
begin with the date command itself: date can take a formatting
string, to modify the way in which the date info is printed. The
formatting string has to be enclosed in quotes, to stop the shell
trying to interpret it before the date command itself gets it.
Try this:
date '+%d%m%y'
you should get back something like 130994. If you want to
punctuate this, just put the characters you would like to use in
the formatting string (NO SLASHES '/'):
date '+%d.%m.%y'
There are lots of token you can use in the formatting string:
have a look at the man page for date to find out about them.
Now, getting this into a file name. Let's say that we want to
create files called report.130994 (or whatever the date is today):
FILENAME=report.`date '+%d%m%y'`
Notice that we are using two sets of quotes here: the inner set
are to protect the formatting string from premature
interpretation; the outer set are to tell the shell to execute
the enclosed command, and substitute the result into the
expression (command substitution).
------------------------------
Subject: Why do some scripts start with #! ... ?
From: chip@@chinacat.unicom.com (Chip Rosenthal)
Date: Tue, 14 Jul 1992 21:31:54 GMT
Chip Rosenthal has answered a closely related question in
comp.unix.xenix in the past.
I think what confuses people is that there exist two different
mechanisms, both spelled with the letter `#'. They both solve the
same problem over a very restricted set of cases -- but they are
none the less different.
Some background. When the UNIX kernel goes to run a program (one
of the exec() family of system calls), it takes a peek at the
first 16 bits of the file. Those 16 bits are called a `magic
number'. First, the magic number prevents the kernel from doing
something silly like trying to execute your customer database
file. If the kernel does not recognize the magic number then it
complains with an ENOEXEC error. It will execute the program only
if the magic number is recognizable.
Second, as time went on and different executable file formats were
introduced, the magic number not only told the kernel *if* it
could execute the file, but also *how* to execute the file. For
example, if you compile a program on an SCO XENIX/386 system and
carry the binary over to a SysV/386 UNIX system, the kernel will
recognize the magic number and say `Aha! This is an x.out
binary!' and configure itself to run with XENIX compatible system
calls.
Note that the kernel can only run binary executable images. So
how, you might ask, do scripts get run? After all, I can type
`my.script' at a shell prompt and I don't get an ENOEXEC error.
Script execution is done not by the kernel, but by the shell. The
code in the shell might look something like:
/* try to run the program */
execl(program, basename(program), (char *)0);
/* the exec failed -- maybe it is a shell script? */
if (errno == ENOEXEC)
execl ("/bin/sh", "sh", "-c", program, (char *)0);
/* oh no mr bill!! */
perror(program);
return -1;
(This example is highly simplified. There is a lot
more involved, but this illustrates the point I'm
trying to make.)
If execl() is successful in starting the program then the code
beyond the execl() is never executed. In this example, if we can
execl() the `program' then none of the stuff beyond it is run.
Instead the system is off running the binary `program'.
If, however, the first execl() failed then this hypothetical shell
looks at why it failed. If the execl() failed because `program'
was not recognized as a binary executable, then the shell tries to
run it as a shell script.
The Berkeley folks had a neat idea to extend how the kernel starts
up programs. They hacked the kernel to recognize the magic number
`#!'. (Magic numbers are 16-bits and two 8-bit characters makes
16 bits, right?) When the `#!' magic number was recognized, the
kernel would read in the rest of the line and treat it as a
command to run upon the contents of the file. With this hack you
could now do things like:
#! /bin/sh
#! /bin/csh
#! /bin/awk -F:
This hack has existed solely in the Berkeley world, and has
migrated to USG kernels as part of System V Release 4. Prior to
V.4, unless the vendor did some special value added, the kernel
does not have the capability of doing anything other than loading
and starting a binary executable image.
Now, lets rewind a few years, to the time when more and more folks
running USG based unices were saying `/bin/sh sucks as an
interactive user interface! I want csh!'. Several vendors did
some value added magic and put csh in their distribution, even
though csh was not a part of the USG UNIX distribution.
This, however, presented a problem. Let's say you switch your
login shell to /bin/csh. Let's further suppose that you are a
cretin and insist upon programming csh scripts. You'd certainly
want to be able to type `my.script' and get it run, even though it
is a csh script. Instead of pumping it through /bin/sh, you want
the script to be started by running:
execl ("/bin/csh", "csh", "-c", "my.script", (char *)0);
But what about all those existing scripts -- some of which are
part of the system distribution? If they started getting run by
csh then things would break. So you needed a way to run some
scripts through csh, and others through sh.
The solution introduced was to hack csh to take a look at the
first character of the script you are trying to run. If it was a
`#' then csh would try to run the script through /bin/csh,
otherwise it would run the script through /bin/sh. The example
code from the above might now look something like:
/* try to run the program */
execl(program, basename(program), (char *)0);
/* the exec failed -- maybe it is a shell script? */
if (errno == ENOEXEC && (fp = fopen(program, "r")) != NULL) {
i = getc(fp);
(void) fclose(fp);
if (i == '#')
execl ("/bin/csh", "csh", "-c", program, (char *)0);
else
execl ("/bin/sh", "sh", "-c", program, (char *)0);
}
/* oh no mr bill!! */
perror(program);
return -1;
Two important points. First, this is a `csh' hack. Nothing has
been changed in the kernel and nothing has been changed in the
other shells. If you try to execl() a script, whether or not it
begins with `#', you will still get an ENOEXEC failure. If you
try to run a script beginning with `#' from something other than
csh (e.g. /bin/sh), then it will be run by sh and not csh.
Second, the magic is that either the script begins with `#' or it
doesn't begin with `#'. What makes stuff like `:' and `: /bin/sh'
at the front of a script magic is the simple fact that they are
not `#'. Therefore, all of the following are identical at the
start of a script:
:
: /bin/sh
<--- a blank line
: /usr/games/rogue
echo "Gee...I wonder what shell I am running under???"
In all these cases, all shells will try to run the script with /bin/sh.
Similarly, all of the following are identical at the start of a script:
#
# /bin/csh
#! /bin/csh
#! /bin/sh
# Gee...I wonder what shell I am running under???
All of these start with a `#'. This means that the script will be
run by csh *only* if you try to start it from csh, otherwise it
will be run by /bin/sh.
(Note: if you are running ksh, substitute `ksh' for
`sh' in the above. The Korn shell is theoretically
compatible with Bourne shell, so it tries to run these
scripts itself. Your mileage may vary on some of the
other available shells such as zsh, bash, etc.)
Obviously, if you've got support for `#!' in the kernel then the
`#' hack becomes superfluous. In fact, it can be dangerous
because it creates confusion over what should happen with `#! /bin/sh'.
The `#!' handling is becoming more and more prevelant. System V
Release 4 picks up a number of the Berkeley features, including
this. Some System V Release 3.2 vendors are hacking in some of
the more visible V.4 features such as this and trying to convince
you this is sufficient and you don't need things like real,
working streams or dynamically adjustable kernel parameters.
XENIX does not support `#!'. The XENIX /bin/csh does have the `#'
hack. Support for `#!' in XENIX would be nice, but I wouldn't
hold my breath waiting for it.
------------------------------
Subject: How do I read characters ... without requiring the user to hit RETURN?
Date: Thu Mar 18 17:16:55 EST 1993
to hit RETURN?
Check out cbreak mode in BSD, ~ICANON mode in SysV.
If you don't want to tackle setting the terminal parameters
yourself (using the "ioctl(2)" system call) you can let the stty
program do the work - but this is slow and inefficient, and you
should change the code to do it right some time:
#include <stdio.h>
main()
{
int c;
printf("Hit any character to continue\n");
/*
* ioctl() would be better here; only lazy
* programmers do it this way:
*/
system("/bin/stty cbreak"); /* or "stty raw" */
c = getchar();
system("/bin/stty -cbreak");
printf("Thank you for typing %c.\n", c);
exit(0);
}
Several people have sent me various more correct solutions to
this problem. I'm sorry that I'm not including any of them here,
because they really are beyond the scope of this list.
You might like to check out the documentation for the "curses"
library of portable screen functions. Often if you're interested
in single-character I/O like this, you're also interested in
doing some sort of screen display control, and the curses library
provides various portable routines for both functions.
------------------------------
Subject: How do I check to see if there are characters to be read ... ?
Date: Thu Mar 18 17:16:55 EST 1993
actually reading?
Certain versions of UNIX provide ways to check whether characters
are currently available to be read from a file descriptor. In
BSD, you can use select(2). You can also use the FIONREAD ioctl,
which returns the number of characters waiting to be read, but
only works on terminals, pipes and sockets. In System V Release
3, you can use poll(2), but that only works on streams. In Xenix
- and therefore Unix SysV r3.2 and later - the rdchk() system call
reports whether a read() call on a given file descriptor will block.
There is no way to check whether characters are available to be
read from a FILE pointer. (You could poke around inside stdio
data structures to see if the input buffer is nonempty, but that
wouldn't work since you'd have no way of knowing what will happen
the next time you try to fill the buffer.)
Sometimes people ask this question with the intention of writing
if (characters available from fd)
read(fd, buf, sizeof buf);
in order to get the effect of a nonblocking read. This is not
the best way to do this, because it is possible that characters
will be available when you test for availability, but will no
longer be available when you call read. Instead, set the
O_NDELAY flag (which is also called FNDELAY under BSD) using the
F_SETFL option of fcntl(2). Older systems (Version 7, 4.1 BSD)
don't have O_NDELAY; on these systems the closest you can get to
a nonblocking read is to use alarm(2) to time out the read.
------------------------------
Subject: How do I find the name of an open file?
Date: Thu Mar 18 17:16:55 EST 1993
In general, this is too difficult. The file descriptor may
be attached to a pipe or pty, in which case it has no name.
It may be attached to a file that has been removed. It may
have multiple names, due to either hard or symbolic links.
If you really need to do this, and be sure you think long
and hard about it and have decided that you have no choice,
you can use find with the -inum and possibly -xdev option,
or you can use ncheck, or you can recreate the functionality
of one of these within your program. Just realize that
searching a 600 megabyte filesystem for a file that may not
even exist is going to take some time.
------------------------------
Subject: How can an executing program determine its own pathname?
Date: Thu Mar 18 17:16:55 EST 1993
Your program can look at argv[0]; if it begins with a "/", it is
probably the absolute pathname to your program, otherwise your
program can look at every directory named in the environment
variable PATH and try to find the first one that contains an
executable file whose name matches your program's argv[0] (which
by convention is the name of the file being executed). By
concatenating that directory and the value of argv[0] you'd
probably have the right name.
You can't really be sure though, since it is quite legal for one
program to exec() another with any value of argv[0] it desires.
It is merely a convention that new programs are exec'd with the
executable file name in argv[0].
For instance, purely a hypothetical example:
#include <stdio.h>
main()
{
execl("/usr/games/rogue", "vi Thesis", (char *)NULL);
}
The executed program thinks its name (its argv[0] value) is
"vi Thesis". (Certain other programs might also think that
the name of the program you're currently running is "vi Thesis",
but of course this is just a hypothetical example, don't
try it yourself :-)
------------------------------
Subject: How do I use popen() to open a process for reading AND writing?
Date: Thu Mar 18 17:16:55 EST 1993
The problem with trying to pipe both input and output to an
arbitrary slave process is that deadlock can occur, if both
processes are waiting for not-yet-generated input at the same
time. Deadlock can be avoided only by having BOTH sides follow a
strict deadlock-free protocol, but since that requires
cooperation from the processes it is inappropriate for a
popen()-like library function.
The 'expect' distribution includes a library of functions that a
C programmer can call directly. One of the functions does the
equivalent of a popen for both reading and writing. It uses ptys
rather than pipes, and has no deadlock problem. It's portable to
both BSD and SV. See the next answer for more about 'expect'.
------------------------------
Subject: How do I sleep() in a C program for less than one second?
Date: Thu Mar 18 17:16:55 EST 1993
The first thing you need to be aware of is that all you can
specify is a MINIMUM amount of delay; the actual delay will
depend on scheduling issues such as system load, and could be
arbitrarily large if you're unlucky.
There is no standard library function that you can count on in
all environments for "napping" (the usual name for short
sleeps). Some environments supply a "usleep(n)" function which
suspends execution for n microseconds. If your environment
doesn't support usleep(), here are a couple of implementations
for BSD and System V environments.
The following code is adapted from Doug Gwyn's System V emulation
support for 4BSD and exploits the 4BSD select() system call.
Doug originally called it 'nap()'; you probably want to call it
"usleep()";
/*
usleep -- support routine for 4.2BSD system call emulations
last edit: 29-Oct-1984 D A Gwyn
*/
extern int select();
int
usleep( usec ) /* returns 0 if ok, else -1 */
long usec; /* delay in microseconds */
{
static struct /* `timeval' */
{
long tv_sec; /* seconds */
long tv_usec; /* microsecs */
} delay; /* _select() timeout */
delay.tv_sec = usec / 1000000L;
delay.tv_usec = usec % 1000000L;
return select( 0, (long *)0, (long *)0, (long *)0, &delay );
}
On System V you might do it this way:
/*
subseconds sleeps for System V - or anything that has poll()
Don Libes, 4/1/1991
The BSD analog to this function is defined in terms of
microseconds while poll() is defined in terms of milliseconds.
For compatibility, this function provides accuracy "over the long
run" by truncating actual requests to milliseconds and
accumulating microseconds across calls with the idea that you are
probably calling it in a tight loop, and that over the long run,
the error will even out.
If you aren't calling it in a tight loop, then you almost
certainly aren't making microsecond-resolution requests anyway,
in which case you don't care about microseconds. And if you did,
you wouldn't be using UNIX anyway because random system
indigestion (i.e., scheduling) can make mincemeat out of any
timing code.
Returns 0 if successful timeout, -1 if unsuccessful.
*/
#include <poll.h>
int
usleep(usec)
unsigned int usec; /* microseconds */
{
static subtotal = 0; /* microseconds */
int msec; /* milliseconds */
/* 'foo' is only here because some versions of 5.3 have
* a bug where the first argument to poll() is checked
* for a valid memory address even if the second argument is 0.
*/
struct pollfd foo;
subtotal += usec;
/* if less then 1 msec request, do nothing but remember it */
if (subtotal < 1000) return(0);
msec = subtotal/1000;
subtotal = subtotal%1000;
return poll(&foo,(unsigned long)0,msec);
}
Another possibility for nap()ing on System V, and probably other
non-BSD Unices is Jon Zeeff's s5nap package, posted to
comp.sources.misc, volume 4. It does require a installing a
device driver, but works flawlessly once installed. (Its
resolution is limited to the kernel HZ value, since it uses the
kernel delay() routine.)
Many newer versions of Unix have a nanosleep function.
------------------------------
Subject: How can I get setuid shell scripts to work?
Date: Thu Mar 18 17:16:55 EST 1993
[ This is a long answer, but it's a complicated and frequently-asked
question. Thanks to Maarten Litmaath for this answer, and
for the "indir" program mentioned below. ]
Let us first assume you are on a UNIX variant (e.g. 4.3BSD or
SunOS) that knows about so-called `executable shell scripts'.
Such a script must start with a line like:
#!/bin/sh
The script is called `executable' because just like a real (binary)
executable it starts with a so-called `magic number' indicating
the type of the executable. In our case this number is `#!' and
the OS takes the rest of the first line as the interpreter for
the script, possibly followed by 1 initial option like:
#!/bin/sed -f
Suppose this script is called `foo' and is found in /bin,
then if you type:
foo arg1 arg2 arg3
the OS will rearrange things as though you had typed:
/bin/sed -f /bin/foo arg1 arg2 arg3
There is one difference though: if the setuid permission bit for
`foo' is set, it will be honored in the first form of the
command; if you really type the second form, the OS will honor
the permission bits of /bin/sed, which is not setuid, of course.
----------
OK, but what if my shell script does NOT start with such a `#!'
line or my OS does not know about it?
Well, if the shell (or anybody else) tries to execute it, the OS
will return an error indication, as the file does not start with
a valid magic number. Upon receiving this indication the shell
ASSUMES the file to be a shell script and gives it another try:
/bin/sh shell_script arguments
But we have already seen that a setuid bit on `shell_script' will
NOT be honored in this case!
----------
Right, but what about the security risks of setuid shell scripts?
Well, suppose the script is called `/etc/setuid_script', starting
with:
#!/bin/sh
Now let us see what happens if we issue the following commands:
$ cd /tmp
$ ln /etc/setuid_script -i
$ PATH=.
$ -i
We know the last command will be rearranged to:
/bin/sh -i
But this command will give us an interactive shell, setuid to the
owner of the script!
Fortunately this security hole can easily be closed by making the
first line:
#!/bin/sh -
The `-' signals the end of the option list: the next argument `-i'
will be taken as the name of the file to read commands from, just
like it should!
---------
There are more serious problems though:
$ cd /tmp
$ ln /etc/setuid_script temp
$ nice -20 temp &
$ mv my_script temp
The third command will be rearranged to:
nice -20 /bin/sh - temp
As this command runs so slowly, the fourth command might be able
to replace the original `temp' with `my_script' BEFORE `temp' is
opened by the shell! There are 4 ways to fix this security hole:
1) let the OS start setuid scripts in a different, secure way
- System V R4 and 4.4BSD use the /dev/fd driver to pass the
interpreter a file descriptor for the script
2) let the script be interpreted indirectly, through a frontend
that makes sure everything is all right before starting the
real interpreter - if you use the `indir' program from
comp.sources.unix the setuid script will look like this:
#!/bin/indir -u
#?/bin/sh /etc/setuid_script
3) make a `binary wrapper': a real executable that is setuid and
whose only task is to execute the interpreter with the name of
the script as an argument
4) make a general `setuid script server' that tries to locate the
requested `service' in a database of valid scripts and upon
success will start the right interpreter with the right
arguments.
---------
Now that we have made sure the right file gets interpreted, are
there any risks left?
Certainly! For shell scripts you must not forget to set the PATH
variable to a safe path explicitly. Can you figure out why?
Also there is the IFS variable that might cause trouble if not
set properly. Other environment variables might turn out to
compromise security as well, e.g. SHELL... Furthermore you must
make sure the commands in the script do not allow interactive
shell escapes! Then there is the umask which may have been set
to something strange...
Etcetera. You should realise that a setuid script `inherits' all
the bugs and security risks of the commands that it calls!
All in all we get the impression setuid shell scripts are quite a
risky business! You may be better off writing a C program instead!
------------------------------
Subject: How can I find out which user or process has a file open ... ?
Date: Thu Mar 18 17:16:55 EST 1993
a particular file system (so that I can unmount it?)
Use fuser (system V), fstat (BSD), ofiles (public domain) or
pff (public domain). These programs will tell you various things
about processes using particular files.
A port of the 4.3 BSD fstat to Dynix, SunOS and Ultrix
can be found in archives of comp.sources.unix, volume 18.
pff is part of the kstuff package, and works on quite a few systems.
Instructions for obtaining kstuff are provided in question 3.10.
I've been informed that there is also a program called lsof. I
don't know where it can be obtained.
Michael Fink <Michael.Fink@uibk.ac.at> adds:
If you are unable to unmount a file system for which above tools
do not report any open files make sure that the file system that
you are trying to unmount does not contain any active mount
points (df(1)).
------------------------------
Subject: How do I keep track of people who are fingering me?
From: jik@cam.ov.com (Jonathan I. Kamens)
From: malenovi@plains.NoDak.edu (Nikola Malenovic)
Date: Thu, 29 Sep 1994 07:28:37 -0400
Generally, you can't find out the userid of someone who is
fingering you from a remote machine. You may be able to
find out which machine the remote request is coming from.
One possibility, if your system supports it and assuming
the finger daemon doesn't object, is to make your .plan file a
"named pipe" instead of a plain file. (Use 'mknod' to do this.)
You can then start up a program that will open your .plan file
for writing; the open will block until some other process (namely
fingerd) opens the .plan for reading. Now you can feed whatever you
want through this pipe, which lets you show different .plan
information every time someone fingers you. One program for
doing this is the "planner" package in volume 41 of the
comp.sources.misc archives.
Of course, this may not work at all if your system doesn't
support named pipes or if your local fingerd insists
on having plain .plan files.
Your program can also take the opportunity to look at the output
of "netstat" and spot where an incoming finger connection is
coming from, but this won't get you the remote user.
Getting the remote userid would require that the remote site be
running an identity service such as RFC 931. There are now three
RFC 931 implementations for popular BSD machines, and several
applications (such as the wuarchive ftpd) supporting the server.
For more information join the rfc931-users mailing list,
rfc931-users-request@kramden.acf.nyu.edu.
There are three caveats relating to this answer. The first is
that many NFS systems won't recognize the named pipe correctly.
This means that trying to read the pipe on another machine will
either block until it times out, or see it as a zero-length file,
and never print it.
The second problem is that on many systems, fingerd checks that
the .plan file contains data (and is readable) before trying to
read it. This will cause remote fingers to miss your .plan file
entirely.
The third problem is that a system that supports named pipes
usually has a fixed number of named pipes available on the
system at any given time - check the kernel config file and
FIFOCNT option. If the number of pipes on the system exceeds the
FIFOCNT value, the system blocks new pipes until somebody frees
the resources. The reason for this is that buffers are allocated
in a non-paged memory.
------------------------------
Subject: Is it possible to reconnect a process to a terminal ... ?
Date: Thu Mar 18 17:16:55 EST 1993
been disconnected, e.g. after starting a program in the background
and logging out?
Most variants of Unix do not support "detaching" and "attaching"
processes, as operating systems such as VMS and Multics support.
However, there are three freely redistributable packages which can
be used to start processes in such a way that they can be later
reattached to a terminal.
The first is "screen," which is described in the
comp.sources.unix archives as "Screen, multiple windows on a CRT"
(see the "screen-3.2" package in comp.sources.misc, volume 28.)
This package will run on at least BSD, System V r3.2 and SCO UNIX.
The second is "pty," which is described in the comp.sources.unix
archives as a package to "Run a program under a pty session" (see
"pty" in volume 23). pty is designed for use under BSD-like
system only.
The third is "dislocate," which is a script that comes with the expect distribution. Unlike the previous two, this should run on all UNIX versions. Details on getting expect can be found in question 3.9 .
None of these packages is retroactive, i.e. you must have
started a process under screen or pty in order to be able to
detach and reattach it.
------------------------------
Subject: Is it possible to "spy" on a terminal ... ?
Date: Wed, 28 Dec 1994 18:35:00 -0500
that's appearing on it on another terminal?
There are a few different ways you can do this, although none
of them is perfect:
* kibitz allows two (or more) people to interact with a shell
(or any arbitary program). Uses include:
- watching or aiding another person's terminal session;
- recording a conversation while retaining the ability to
scroll backwards, save the conversation, or even edit it
while in progress;
- teaming up on games, document editing, or other cooperative
tasks where each person has strengths and weakness that
complement one another.
kibitz comes as part of the expect distribution. See question 3.9.
kibitz requires permission from the person to be spyed upon. To
spy without permission requires less pleasant approaches:
* You can write a program that rummages through Kernel structures
and watches the output buffer for the terminal in question,
displaying characters as they are output. This, obviously, is
not something that should be attempted by anyone who does not
have experience working with the Unix kernel. Furthermore,
whatever method you come up with will probably be quite
non-portable.
* If you want to do this to a particular hard-wired terminal all
the time (e.g. if you want operators to be able to check the
console terminal of a machine from other machines), you can
actually splice a monitor into the cable for the terminal. For
example, plug the monitor output into another machine's serial
port, and run a program on that port that stores its input
somewhere and then transmits it out *another* port, this one
really going to the physical terminal. If you do this, you have
to make sure that any output from the terminal is transmitted
back over the wire, although if you splice only into the
computer->terminal wires, this isn't much of a problem. This is
not something that should be attempted by anyone who is not very
familiar with terminal wiring and such.
* The latest version of screen includes a multi-user mode.
Some details about screen can be found in question 4.10.
* If the system being used has streams (SunOS, SVR4), the advise
program that was posted in volume 28 of comp.sources.misc can
be used. AND it doesn't requirethat it be run first (you do
have to configure your system in advance to automatically push
the advise module on the stream whenever a tty or pty is opened).
------------------------------
Subject: Can shells be classified into categories?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500
In general there are two main class of shells. The first class
are those shells derived from the Bourne shell which includes sh,
ksh, bash, and zsh. The second class are those shells derived
from C shell and include csh and tcsh. In addition there is rc
which most people consider to be in a "class by itself" although
some people might argue that rc belongs in the Bourne shell class.
With the classification above, using care, it is possible to
write scripts that will work for all the shells from the Bourne
shell category, and write other scripts that will work for all of
the shells from the C shell category.
------------------------------
Subject: How do I "include" one shell script from within another shell script?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500
All of the shells from the Bourne shell category (including rc)
use the "." command. All of the shells from the C shell category
use "source".
------------------------------
Subject: Do all shells have aliases? Is there something else that can be used?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500
All of the major shells other than sh have aliases, but they
don't all work the same way. For example, some don't accept
arguments.
Although not strictly equivalent, shell functions (which exist in
most shells from the Bourne shell category) have almost the same
functionality of aliases. Shell functions can do things that
aliases can't do. Shell functions did not exist in bourne shells
derived from Version 7 Unix, which includes System III and BSD 4.2.
BSD 4.3 and System V shells do support shell functions.
Use unalias to remove aliases and unset to remove functions.
------------------------------
Subject: How are shell variables assigned?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500
The shells from the C shell category use "set variable=value" for
variables local to the shell and "setenv variable value" for
environment variables. To get rid of variables in these shells
use unset and unsetenv. The shells from the Bourne shell
category use "variable=value" and may require an "export
VARIABLE_NAME" to place the variable into the environment. To
get rid of the variables use unset.
------------------------------
Subject: How can I tell if I am running an interactive shell?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
From: dws@ssec.wisc.edu (DaviD W. Sanderson)
Date: Fri, 23 Oct 92 11:59:19 -0600
In the C shell category, look for the variable $prompt.
In the Bourne shell category, you can look for the variable $PS1,
however, it is better to check the variable $-. If $- contains
an 'i', the shell is interactive. Test like so:
case $- in
*i*) # do things for interactive shell
;;
*) # do things for non-interactive shell
;;
esac
------------------------------
Subject: What "dot" files do the various shells use?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
From: tmb@idiap.ch (Thomas M. Breuel)
Date: Wed, 28 Oct 92 03:30:36 +0100
Although this may not be a complete listing, this provides the
majority of information.
csh
Some versions have system-wide .cshrc and .login files. Every
version puts them in different places.
Start-up (in this order):
.cshrc - always; unless the -f option is used.
.login - login shells.
Upon termination:
.logout - login shells.
Others:
.history - saves the history (based on $savehist).
tcsh
Start-up (in this order):
/etc/csh.cshrc - always.
/etc/csh.login - login shells.
.tcshrc - always.
.cshrc - if no .tcshrc was present.
.login - login shells
Upon termination:
.logout - login shells.
Others:
.history - saves the history (based on $savehist).
.cshdirs - saves the directory stack.
sh
Start-up (in this order):
/etc/profile - login shells.
.profile - login shells.
Upon termination:
any command (or script) specified using the command:
trap "command" 0
ksh
Start-up (in this order):
/etc/profile - login shells.
.profile - login shells; unless the -p option is used.
$ENV - always, if it is set; unless the -p option is used.
/etc/suid_profile - when the -p option is used.
Upon termination:
any command (or script) specified using the command:
trap "command" 0
bash
Start-up (in this order):
/etc/profile - login shells.
.bash_profile - login shells.
.profile - login if no .bash_profile is present.
.bashrc - interactive non-login shells.
$ENV - always, if it is set.
Upon termination:
.bash_logout - login shells.
Others:
.inputrc - Readline initialization.
zsh
Start-up (in this order):
.zshenv - always, unless -f is specified.
.zprofile - login shells.
.zshrc - interactive shells, unless -f is specified.
.zlogin - login shells.
Upon termination:
.zlogout - login shells.
rc
Start-up:
.rcrc - login shells
------------------------------
Subject: I would like to know more about the differences ... ?
From: wicks@dcdmjw.fnal.gov (Matthew Wicks)
Date: Wed, 7 Oct 92 14:28:18 -0500
various shells. Is this information available some place?
A very detailed comparison of sh, csh, tcsh, ksh, bash, zsh, and
rc is available via anon. ftp in several places:
cs.uwp.edu (131.210.1.4):pub/vi/docs/shell-100.BetaA.Z
utsun.s.u-tokyo.ac.jp:misc/vi-archive/docs/shell-100.BetaA.Z
This file compares the flags, the programming syntax,
input/output redirection, and parameters/shell environment
variables. It doesn't discuss what dot files are used and the
inheritance for environment variables and functions.
------------------------------
Subject: Disclaimer, introduction and acknowledgements.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Tue Aug 15 15:14:00 EDT 1995
X-Version: 2.9
NOTE TO READERS: I would like to update this FAQ with WWW pointers
for the various Unices I mention. Don't hesitate to send them along,
I'll eventually get around to updating this part. Email: lew@bnr.ca
The following is offered with no guarantee as to accuracy or
completeness. I have done what I can in the time available,
often with conflicting information, and it still is very much work
in progress. I hope to keep improving this summary. Comments and
corrections welcome: lew@bnr.ca.
First a short definition. By Unix we mean an operating system
typically written in C, with a hierarchical file system,
integration of file and device I/O, whose system call interface
includes services such as fork(), pipe(), and whose user
interface includes tools such as cc, troff, grep, awk, and a
choice of shell. Note that UNIX was a registered trademark of USL
(AT&T), now of X/Open, but will be used here in its generic sense.
Most Unices (the more common plural form) are derived more or
less directly from AT&T (now Novell) code (some code from the first C
version is presumably still left in most), but there are also clones
(i.e. Unix-compatible systems with no AT&T code).
In addition, there are also Unix-like environments (e.g. VOS)
sitting on top of other OSs, and OSs inspired from Unix (yes,
even DOS!). These are not covered here. Little on real-time
Unices yet (although more is planned).
Unix comes in an incredible variety of flavors. This is to a
large extent due to availability of sources and the ease of
porting and modifying Unix. Typically, a vendor of Unix will
start with one basic flavor (see below), take ideas/code from the
other major flavor, add and change many things, etc. This
results in yet another new Unix flavor. Today, there are
literally hundreds of Unices available, the closest thing to
standard Unix being (by definition) System V.
This answer was put together mostly from information on the net
and email. Some specific sources are also mentioned in the
appropriate sections.
Acknowledgements: (in addition to references): pat@bnr.ca,
guy@auspex.com, pen@lysator.liu.se, mikes@ingres.com,
mjd@saul.cis.upenn.edu, root%candle.uucp@ls.com, ee@atbull.bull.co.at,
Aaron_Dailey@stortek.com, ralph@dci.pinetree.org, sbdah@mcshh.hanse.de,
macmach@andrew.cmu.edu, jwa@alw.nih.gov [4.4BSD], roeber@axpvms.cern.ch,
bob@pta.pyramid.com.au, bad@flatlin.ka.sub.org, m5@vail.tivoli.com,
dan@fch.wimsey.bc.ca, jlbrand@uswnvg.com, jpazer@usl.com,
ym@satelnet.org, merritt@gendev.slc.paramax.com, quinlan@yggdrasil.com,
steve@rudolph.ssd.csd.harris.com, bud@heinous.isca.uiowa.edu,
pcu@umich.edu, quinlan@yggdrasil.com, Dan_Menchaca@quickmail.apple.com,
D.Lamptey@sheffield.ac.uk, derekn@vw.ece.cmu.edu, gordon@PowerOpen.org,
romain@pyramid.com, rzm@dain.oso.chalmers.se, chen@adi.com,
tbm@tci002.uibk.ac.at, sllewis@nando.net, edwin@modcomp.demon.co.uk,
many that I forgot, and all the other folks whose posts I read. Many
thanks!
------------------------------
Subject: A very brief look at Unix history.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6
Unix history goes back to 1969 and the famous "little-used PDP-7
in a corner" on which Ken Thompson, Dennis Ritchie (the R in K&R)
and others started work on what was to become Unix. The name
"Unix" was intended as a pun on Multics (and was written "Unics"
at first -- UNiplexed Information and Computing System).
For the first 10 years, Unix development was essentially confined
to Bell Labs. These initial versions were labeled "Version n" or
"Nth Edition" (of the manuals), and were for DEC's PDP-11 (16
bits) and later VAXen (32 bits). Some significant versions
include:
V1 (1971): 1st Unix version, in assembler on a PDP-11/20.
Included file system, fork(), roff, ed. Was used as a text
processing tool for preparation of patents. Pipe() appeared
first in V2!
V4 (1973): Rewritten in C, which is probably the most
significant event in this OS's history: it means Unix can be
ported to a new hardware in months, and changes are easy. The
C language was originally designed for the Unix operating
system, and hence there is a strong synergy between C and Unix.
V6 (1975): First version of Unix widely available outside
Bell Labs (esp. in universities). This was also the start of
Unix diversity and popularity. 1.xBSD (PDP-11) was derived
from this version. J. Lions published "A commentary on the
Unix Operating System" based on V6.
V7 (1979): For many, this is the "last true Unix", an
"improvement over all preceding and following Unices"
[Bourne]. It included full K&R C, uucp, Bourne shell. V7 was
ported to the VAX as 32V. The V7 kernel was a mere 40
Kbytes!
Here (for reference) are the system calls of V7:
_exit, access, acct, alarm, brk, chdir, chmod, chown,
chroot, close, creat, dup, dup2, exec*, exit, fork, fstat,
ftime, getegid, geteuid, getgid, getpid, getuid, gtty,
indir, ioctl, kill, link, lock, lseek, mknod, mount,
mpxcall, nice, open, pause, phys, pipe, pkoff, pkon,
profil, ptrace, read, sbrk, setgid, setuid, signal, stat,
stime, stty, sync, tell, time, times, umask, umount,
unlink, utime, wait, write.
These Vn versions were developed by the Computer Research Group
(CRG) of Bell Labs. Another group, the Unix System Group (USG),
was responsible for support. A third group at Bell Labs was also
involved in Unix development, the Programmer's WorkBench (PWB),
to which we owe, for example, sccs, named pipes and other
important ideas. Both groups were merged into Unix System
Development Lab in 1983.
Another variant of Unix was CB Unix (Columbus Unix) from the Columbus
branch of Bell Labs, responsible of Operations Support Systems. Its
main contribution was parts of SV IPC.
Work on Unix continued at Bell Labs in the 1980s. The V series
was further developed by the CRG (Stroustrup mentions V10 in the
2nd edition of his book on C++), but we don't seem to hear much
about this otherwise. The company now responsible for Unix
(System V) is called Unix System Laboratories (USL) and is
majority-owned by AT&T. Novell has bought USL (early 93)!
Novell has given rights to the "UNIX" trademark to X/Open (late 93).
But much happened to Unix outside AT&T, especially at Berkeley
(where the other major flavor comes from). Vendors (esp. of
workstations) also contributed much (e.g. Sun's NFS).
The book "Life with Unix" by Don Libes and Sandy Ressler is
fascinating reading for anyone interested in Unix, and covers a
lot of the history, interactions, etc.. Much in the present
section is summarized from this book.
------------------------------
Subject: Main Unix flavors.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Mon Jan 9 16:59:14 EST 1995
X-Version: 2.7
The following is very much an early '90s view.
Until recently, there were basically two main flavors of Unix:
System V (five) from AT&T, and the Berkeley Software Distribution
(BSD). SVR4 is essentially a merge of these two flavors. End
'91, OSF/1 from the Open Software Foundation was released (as a
direct competitor to System V) and may (future will tell) change
this picture.
The following lists the main releases and features of System V,
BSD and OSF/1.
System V from AT&T. Typical of Intel hardware. Most often
ported Unix, typically with BSD enhancements (csh, job
control, termcap, curses, vi, symbolic links). System V
evolution is now overseen by Unix International (UI). UI
members include AT&T, Sun, ....
Newsgroup: comp.unix.sysv[23]86. Main releases:
- System III (1982): first commercial Unix from AT&T
- FIFOs (named pipes) (later?)
- System V (1983):
- IPC package (shm, msg, sem)
- SVR2 (1984):
- shell functions (sh)
- SVID (System V Interface Definition)
- SVR3 (1986) for ? platforms:
- STREAMS (inspired by V8), poll(), TLI (network software)
- RFS
- shared libs
- SVID 2
- demand paging (if hardware supports)
- SVR3.2:
- merge with Xenix (Intel 80386)
- networking
- SVR4 (1988), mainstream of Unix implementations, merge of
System V, BSD, and SunOS.
- From SVR3: sysadmin, terminal I/F, printer (from BSD?),
RFS, STREAMS, uucp
- From BSD: FFS, TCP/IP, sockets, select(), csh
- From SunOS: NFS, OpenLook GUI, X11/NeWS, virtual memory
subsystem with memory-mapped files, shared libraries
(!= SVR3 ones?)
- ksh
- ANSI C
- Internationalization (8-bit clean)
- ABI (Application Binary Interface -- routines instead of traps)
- POSIX, X/Open, SVID3
- SVR4.1
- async I/O (from SunOS?)
- SVR4.2 (based on SVR4.1ES)
- Veritas FS, ACLs
- Dynamically loadable kernel modules
- Future:
- SVR4 MP (multiprocessor)
- Use of Chorus microkernel?
Berkeley Software Distribution (BSD). Typical of VAXen, RISCs,
many workstations. More dynamic, research versions now than
System V. BSD is responsible for much of the popularity of
Unix. Most enhancements to Unix started here. The group
responsible at UCB (University of California at Berkeley) is
the Computer System Research Group (CSRG). They closed down
in 1992. Newsgroup: comp.unix.bsd. Main releases:
(much reorganized wrt dates and releases, hope it's converging)
- 2.xBSD (1978) for PDP-11, still of significance? (2.11BSD
was released in 1992!).
- csh
- 3BSD (1978):
- virtual memory
- 4.?BSD:
- termcap, curses
- vi
- 4.0BSD (1980):
- 4.1BSD (?): base of later AT&T CRG versions
- job control
- automatic kernel config
- vfork()
- 4.2BSD (1983):
- TCP/IP, sockets, ethernet
- UFS: long file names, symbolic links
- new reliable signals (4.1 reliable signals now in SVR3)
- select()
- 4.3BSD (1986) for VAX, ?:
- 4.3 Tahoe (1988): 4.3BSD with sources, support for Tahoe
(32-bit supermini)
- Fat FFS
- New TCP algorithms
- 4.3 Reno (1990) for VAX, Tahoe, HP 9000/300:
- most of P1003.1
- NFS (from Sun)
- MFS (memory file system)
- OSI: TP4, CLNP, ISODE's FTAM, VT and X.500; SLIP
- Kerberos
- Net1 (?) and Net2 (June 1991) tapes: that portion of BSD which
requires no USL copyright
- 4.4BSD (alpha June 1992) for HP 9000/300, Sparc, 386, DEC, others;
neither VAX nor Tahoe; two versions, lite (~Net2 contents plus,
fixes and new architectures) and encumbered (everything, requires
USL license):
- new virtual memory system (VMS) based on Mach 2.5
- virtual filesystem interface, log-structured filesystem, size
of local filesystem up to 2^63, NFS (freely redistributable,
works with Sun's, over UDP or TCP)
- ISO/OSI networking support (based on ISODE): TP4/CLNP/802.3 and
TP0/CONS/X.25, session and above in user space; FTAM, VT, X.500.
- most of POSIX.1 (esp. new terminal driver a la SV), much of
POSIX.2, improved job control; ANSI C headers
- Kerberos integrated with much of the system (incl. NFS)
- TCP/IP enhancements (incl. header prediction, SLIP)
- important kernel changes (new system call convention, ...)
- other improvements: FIFOs, byte-range file locking
Official 4.4BSD release was expected within 6 months of above.
The Open Software Foundation (OSF) released its Unix called OSF/1
end of 1991. Still requires an SVR2 license.
Compatible/compliant with SVID 2 (and 3 coming), POSIX,
X/Open, etc.. OSF members include Apollo, Dec, HP, IBM, ....
- OSF/1 (1991):
- based on Mach 2.5 kernel
- symmetric multiprocessing, parallelized kernel, threads
- logical volumes, disk mirroring, UFS (native), S5 FS, NFS
- enhanced security (B1 with some B2, B3; or C2), 4.3BSD admin
- STREAMS, TLI/XTI, sockets
- shared libs, dynamic loader (incl. kernel)
- Motif GUI
- Release 1.3 (Jun 94)
- Based on MACH 3.0 Micro-kernel
- Conformant with current draft of Specification 1170
(considered for standardization in X/Open's Fast Track process)
- Data Capture I/F, Common Data Link I/F,
- ISO 10646 and 64-bit support.
- OSF/1 MK (mikrokernel) based on Mach 3.0
This list of major flavors should probably also include Xenix
(Microsoft) which has been the basis for many ports. Derived from V7,
S III and finally System V, it is similar externally but significantly
changed internally (performance-tuned for micros).
Two very good books describe the internals of the two main flavors.
These are:
- System V: "Design of the Unix Operating System", M.J. Bach.
- BSD: "Design and Implementation of the 4.3BSD Unix Operating System",
Leffler, McKusick, Karels, Quaterman.
For a good introduction to OSF/1 (not quite as technical as the
previous two), see: "Guide to OSF/1, A Technical Synopsis",
published by O'Reilly. On SunOS, "Virtual Memory Architecture in
SunOS" and "Shared Libraries in SunOS" in Summer 1989 USENIX
Proceedings.
A good set of articles on where Unix is going is "Unix Variants"
in the Apr 92 issue of Unix Review. Other good sources of
information include the bsd-faq file, and many of the newsgroups
mentioned in the text.
------------------------------
Subject: Main Players and Unix Standards.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Mon Jan 21 16:59:14 EST 1995
X-Version: 2.8
The more important players in the Unix scene currently (early '95)
are (corrections most welcome, these are new bytes):
- Novell who bought USL (early 93) and now has the source code.
- X/Open who has the branding rights to "UNIX" trademark.
- OSF, both as developer of OSF/1 and Motif, and as organization
overseeing COSE (OSF's new working model). OSF was reorganized in
1994 (and Sun joined), relationship with X/Open has been formalized.
- IEEE with POSIX, LAN standards.
- PowerOpen [IBM, Apple, Motorola, Bull, others] promoting the PowerPC.
Do not confuse with graphical environment of same name.
The following briefly describes the more important standards
relevant to Unix.
- IEEE:
- 802.x (LAN) standards (LLC, ethernet, token ring, token bus)
- POSIX (ISO 9945?): Portable Operating System I/F (Unix, VMS
and OS/2!) (only ? have been finalized at this point)
- 1003.1: library procedures (mostly system calls) -- roughly V7
except for signals and terminal I/F (1990)
- 1003.2: shell and utilities
- 1003.3: test methods and conformance
- 1003.4: real-time: binary semaphores, process memory
locking, memory-mapped files, shared memory,
priority scheduling, real-time signals, clocks and
timers, IPC message passing, synchronized I/O,
asynchronous I/O, real-time files
- 1003.5: Ada language bindings
- 1003.6: security
- 1003.7: system admin (incl. printing)
- 1003.8: transparent file access
- 1003.9: FORTRAN language bindings
- 1003.10: super computing
- 1003.12: protocol-independent I/Fs
- 1003.13: real-time profiles
- 1003.15: supercomputing batch I/Fs
- 1003.16: C-language bindings (?)
- 1003.17: directory services
- 1003.18: POSIX standardized profile
- 1003.19: FORTRAN 90 language bindings
- X/Open (consortium of vendors, founded 1984):
- X/Open Portability Guides (XPGn):
- XPG2 (1987), strong SV influence
Vol 1: commands and utilities
Vol 2: system calls and libraries
Vol 3: terminal I/F (curses, termio), IPC (SV),
internationalization
Vol 4: programming languages (C, COBOL!)
Vol 5: data management (ISAM, SQL)
- XPG3 (1989) adds: X11 API
- XPG4 (1992) adds: XTI? 22 components
- XOM series of interfaces:
- XOM (X/Open Object Management) generic I/F mechanisms for
following
- XDS (X/Open Directory Service)
- XMH (X/Open Mail ??)
- XMP (X/Open Management Protocols) -- not Bull's CM API?
- X/Open now has the rights to the "UNIX" trademark (late 93);
- "Spec 1170"
- This specification is being prepared describing a common API
to which vendors wanting to use the name "UNIX" will have to
comply (when test suites are available). Merge of SVID,
OSF's AES and other stuff.
- AT&T
(is this still relevant in 1994? Who is now responsible for SVID,
TLI, APLI?)
- System V Interface Definition (SVID)
- SVID1 (1985, SVR2)
Vol 1: system calls and libraries (similar to XPG2.1)
- SVID2 (1986, SVR3)
Vol 1: system calls and libraries (base, kernel extensions)
Vol 2: commands and utilities (base, advanced, admin, software
development), terminal I/F
Vol 3: terminal I/F (again), STREAMS and TLI, RFS
- SVID3 (19??, SVR4) adds
Vol 4: ?? &c
- APIs
- Transport Library Interface (TLI)
- ACSE/Presentation Library Interface (APLI)
- COSE (COmmon Open Software Environment) [IBM, HP, SunSoft, others]:
objective is to bring different Unix platforms closer together.
Initiatives in the following areas:
- desktop environments
- application API (aka Spec 1170 -- a single programming i/f) --
probably the more important achievement at this point: eliminates
differences between SCO, AIX, Solaris, HP-UX, UnixWare.
- distributed computing services (OSF's DCE and SunSoft's ONC)
- object technologies (OMG's CORBA)
- graphics
- multimedia
- systems management
- PowerOpen Environment (POE) promoted by the PowerOpen association
(POA). A standard for Unix-like OSs running on PowerPC chip. Defines:
- an API (application programming i/f, derived from AIX, conforms to
POSIX, XPG4, Motif, &c) and
- an ABI (application binary i/f), a distinguishing factor from other
standards such as POSIX, XPG4, &c.. Any POE-compliant system will
be able to run all POE software.
Key features:
- based on the PowerPC architecture
- hardware bus independence
- system implementations can range from laptops to supercomputers
- requires a multi-user, multi-tasking operating system
- networking support
- X windows extension, Motif
- conformance tested and certified by an independent party (POA)
AIX 4.1.1 will be PowerOpen compliant. MacOS isn't and won't be.
[above adapted from the powerpc-faq from comp.sys.powerpc]
IBM is involved in both COSE and POE. How will the two interact?
------------------------------
Subject: Identifying your Unix flavor.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6
This section lists a number of things you can look at in
attempting to identify the base flavor of your Unix. Given the
significant exchange of code and ideas between the various
flavors and the many changes made by vendors, any statement such
as "this Unix is an SVR2" is at best a statistical statement
(except for some SVRn ports). Also many Unices offer most of
both worlds (either mixed as in SunOS or strictly separated as in
Apollo?). So this section is perhaps not very useful...
The list of features in previous sections can also help. For
example, if a system has a poll(2) but no select(2), it is highly
probable that it is derived from SVR3. Also the name of the OS
can provide a clue, as well as the logon message (e.g. SGI's
"IRIX SVR3.3.2") or the output of "uname -a" command. Available
commands can also provide hints but this is probably less
reliable than kernel features. For example, the type of terminal
initialization (inittab or ttys) is a more reliable indicator
than the print subsystem.
Feature Typical in SVRx Typical in xBSD
kernel name /unix /vmunix
terminal init /etc/inittab /etc/ttys (only getty to 4.3)
boot init /etc/rc.d directories /etc/rc.* files
mounted FSs /etc/mnttab /etc/mtab
usual shell sh, ksh csh, #! hack
native FS S5 (blk: 512-2K) UFS (blk: 4K-8K)
file names <= 14 bytes file names < 255 bytes
groups need newgrp(1) automatic membership
SVR4: multiple groups
print subsystem lp, lpstat, cancel lpr, lpq, lprm (lpd daemon) ??
terminal control termio, terminfo, termios (sgtty before 4.3reno)
SVR4: termios (POSIX) termcap
job control >= SVR4 yes
ps command ps -ef ps -aux
multiple wait poll select
string fcns memset, memcpy bzero, bcopy
process mapping /proc (SVR4)
As we move to the late '90s, this is probably less and less relevant.
------------------------------
Subject: Brief notes on some well-known (commercial/PD) Unices.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Tue Aug 15 15:14:00 EDT 1995
X-Version: 2.9
(I am not at all satisfied with this section, unfortunately I
have neither the time nor the documents to make it much better
(wrt contents). Should only list Unices known by a reasonably
wide audience. Small and non-US Unices welcome, e.g. Eurix. In
need of reformatting)
This section lists (in alphabetical order) some of the better
known Unices along with a brief description of their nature.
Unfortunately, it's out-of-date almost by definition...
(sorted alpha, ignoring numbers and other chars)
AIX: IBM's Unix, based on SVR2 (later up to SVR3.2?) with varying
degrees of BSD extensions, for various hardwares. Proprietary
system admin (SMIT). Both 850 and Latin-1 CPs. Quite
different from most Unices and among themselves.
Newsgroup: comp.unix.aix.
- 1.x (for 386 PS/2)
- 2.x (for PC RTs)
- 3.x (for RS/6000), paging kernel, logical volume manager, i18n;
3.2 adds TLI/STREAMS. SV-based with many enhancements.
4.1 is latest (includes support for PowerPC?)
- AIX/ESA, runs native on S/370 and S/390 mainframes, based on OSF/1.
AIX was to have been base for OSF/1 until Mach was chosen instead.
I hope this subsection is converging :-)
AOS (IBM): 4.3BSD port to IBM PC RT (for educational institutes).
Don't confuse with DG's proprietary OS of same name.
Arix: SV
A3000UX (Commodore): 68030-based SVR4 Unix (?) for the Amiga.
A/UX (Apple): SV with Berkeley enhancements, NFS, Mac GUI. System 6
(later System 7) runs as guest of A/UX (opposite of MachTen).
Newsgroup: comp.unix.aux.
- 2.0: SVR2 with 4.2BSD, system 6 Mac applications.
- 3.0 (1992): SVR2.2 with 4.3BSD and SVR3/4 extensions; X11R4,
MacX, TCP/IP, NFS, NIS, RPC/XDR, various shells, UFS or S5FS.
System 7 applications.
- 4.0 will have/be OSF/1. But I hear Apple has decided to drop
A/UX (will go for AIX now that they're together with IBM on
the PPC)
3B1 (680x0): SV-based, done by Convergent for AT&T.
Newsgroup: comp.sys.3b1.
BNR/2: stands for BSD Net/2 Release? Includes NetBSD/1, FreeBSD.
BOS for Bull's DPX/2 (680x0)
- V1 (1990): SVR3 with BSD extensions (FFS, select, sockets),
symmetric MP, X11R3
- V2 (1991): adds job control, disk mirroring, C2 security,
DCE extensions
- There's also BOS/X, and AIX-compatible Unix for Bull's PPC
workstations. How it relates to above two is unknown.
386BSD: Jolitz's port of Net/2 software. Posix, 32-bit, still in alpha
(now version 0.1).
BSD/386 (80386): from BSDI, with source (augmented Net2 software)
Newsgroup: comp.unix.bsd.
Chorus/MiXV: Unix SVR3.2 (SVR4) over Chorus nucleus, ABI/BCS.
Coherent (Mark Williams Company): For 80286. Unix clone compatible with
V7, some SVR2 (IPC). V4.0 is 32-bit. Newsgroup: comp.os.coherent.
Mark Williams closed down early '95.
Consensys: SVR4.2
CTIX: SV-based, from Convergent
D-NIX: SV
DC/OSx (Pyramid): SVR4. Newsgroup: comp.sys.pyramid.
DELL UNIX [DELL Computer Corp.]: SVR4
DomainIX: see DomainOS below.
DomainOS (Apollo, now HP): proprietary OS; layered on top is BSD4.3 and
SVR3 (a process can use either, neither or both). Development now
stopped, some features now in OSF/1 (and NT). Now at SR10.4.
Name for SR9.* was DomainIX. Newsgroup: comp.sys.apollo.
DVIX (NT's DVS): SVR2
DYNIX (Sequent): 4.2BSD-based
DYNIX/PTX: SVR3-based
EP/IX (Control Data Corp.): for MIPS 2000/3000/6000/4000; based on
RISC/OS 4 and 5, POSIX-ABI-compliant. SVR3, SVR4 and BSD modes.
Esix (80386): pure SVR4, X11, OpenLook (NeWS), Xview
Eurix (80?86): SVR3.2 (Germany)
FreeBSD: 386bsd 0.1 with the patchkit applied, and many updated
utilities.
FTX: Stratus fault-tolerant OS (68K or i860-i960 hardware)
Generics UNIX (80386): SVR4.03 (Germany)
GNU Hurd (?): vaporware from the Free Software Foundation (FSF):
Unix emulator over Mach 3.0 kernel. Many GNU tools are very
popular (emacs) and used in the PD Unices.
HELIOS (Perihelion Software): for INMOS transputer and many other
platforms.
HP-UX (HP): old from S III (SVRx), now SVR2 (4.2BSD?) with SV utilities
(they have trouble making up their minds).
- 6.5: SVR2
- 7.0: SVR3.2, symlinks
- 7.5
- 8.0: BSD based? for HP-9000 CISC (300/400) and RISC (800/700),
shared libs
- 9.0: includes DCE
Interactive SVR3.2 (80x86): pure SVR3. Interactive has been bought
by Sun; will their system survive Solaris?
Idris: first Unix clone by Whitesmith. A small Unix? For INMOS
transputer and others?.
IRIX (SGI): Version 4: SVR3.2, much BSD. Version 5.x (current is 5.2)
is based on SVR4. Newsgroup: comp.sys.sgi.
Linux (386/486/586): Unix under GPL (not from FSF, though). Available
with sources. POSIX compliant w/ SysV and BSD extensions. Being
ported to Alpha/AXP and PowerPC (ports for 680x0 Amigas and Ataris
already exist; a port is also being done to the MIPS/4000).
Newsgroup: comp.os.linux.{admin,announce,development,help,misc}.
MacBSD, ?: works on Mac II (directly on H/W).
MachTen, Tenon Intersystems: runs as a guest under MacOS; 4.3BSD
environment with TCP, NFS. Scaled down version: MachTen Personal.
MacMach (Mac II): 4.3BSD over Mach 3.0 microkernel, X11, Motif, GNU
software, sources, experimental System 7 as Mach task. Complete
with all sources (need Unix license).
Mach386: from Mt Xinu. Based on Mach 2.5, with 4.3BSD-Tahoe
enhancements. Also 2.6 MSD (Mach Source Distribution).
Microport (80x86): pure SVR4, X11, OpenLook GUI
Minix (80x86, Atari, Amiga, Mac): Unix clone compatible with V7.
Sold with sources. Being POSIXified (sp?). For PCs, and surely
many others (eg. INMOS transputer). Newsgroup: comp.os.minix.
MipsOS: SVish (RISC/OS, now dropped, was BSDish)
more/BSD (VAX, HP 9000/300): Mt Xinu's Unix, based on 4.3BSD-Tahoe.
NCR UNIX: SVR4 (4.2?)
Net/2 tape (from Berkeley, 1991): BSD Unix, essentially compatible with
4.3BSD, includes only sources free of AT&T code, no low-level code.
See 386BSD and BSD/386 above.
NetBSD 0.8: is actually 386bsd in a new suit. Ported to [34]86, MIPS,
Amiga, Sun, Mac. What is relation to Net/2?
- 1.0 came out in '94.
NEXTSTEP (Intel Pentium and 86486, Hewlett-Packard PA-RISC, NeXT 68040):
BSD4.3 over Mach kernel, own GUI.
- 1.x, 2.0, 2.1, 2.2, 3.0, 3.1 (old)
- 3.2 (current version,
Intel Pentium and 86486,
Hewlett-Packard PA-RISC,
NeXT 68040)
- 3.3 (shipping; SPARC-version available)
- 4.0 (to be announced, will include Sun SPARC version and
will be OpenStep compliant
- no NEXTSTEP for PowerPC or DEC Alpha yet announced (are there plans?
NEWS-OS (Sony)
- 3.2
OSF/1 (DEC): DEC's port of OSF/1. I think this is now (4/93) available
on DEC's latest Alpha AXP (64-bit machine).
OSx (Pyramid): Dualport of both SysV.3 and BSD4.3. Newsgroup:
comp.sys.pyramid.
PC-IX (IBM 8086): SV
Plan 9 (AT&T): announced 1992, complete rewrite, not clear how close to
Unix it is. Key points: distributed, very small, various hardwares
(Sun, Mips, Next, SGI, generic hobbit, 680x0, PCs), C (not C++ as
rumors had it), new compiler, "8 1/2" window system (also very
small), 16-bit Unicode, CPU/file servers over high speed nets.
SCO Xenix (80x86): Versions for XT (not robust!), 286, 386 (with demand
paging). Today bulk of code is from System V. Stable product.
SCO Unix (80x86): SVR3.2 (stopped taking USL source at this point).
Sinix [Siemens]: System V base.
Solaris (Sparc, x86):
- 1.0: essentially same as SunOS 4.1.1, with OpenWindows 2.0 and
DeskSet utilities.
- 1.0.1: SunOS 4.1.2 with multiprocessing (kernel not multithreaded);
not for 386
- 2.0: (initially announced as SunOS 5.0 in 1988) based on SVR4
(with symmetric MP?), will include support for 386; with
OpenWindows 3.0 (X11R4) and OpenLook, DeskSet, ONC, NIS. Both
a.out (BSD) and elf (SVR4) formats. Kerberos support. Compilers
unbundled!
- Solaris is OpenStep compliant (non-NeXT, but with NEXTSTEP API)
with latest (1994?) version.
- Sun will ship its OpenStep-implementation with project DOE for
Solaris. First versions will be for SPARC-based Suns, but a
version for Solaris 2.4 for x86 and PowerPC will appear later.
SunOS (680x0, Sparc, i386): based on 4.3BSD, includes much from
System V. Main Sun achievements: NFS (1984), SunView (1985), NeWS
(1986, postscript imaging, now in OpenWindows), OpenLook GUI standard,
OpenWindows (NeWS, X11, SunView!). Newsgroup: comp.sys.sun.*.
- 3.x: SV IPC package, FIFOs
- 4.0.3: lightweight processes, new virtual mem, shared libs
- 4.1: STREAMS & TLI, 8-bit clean?, async I/O, ms-dos file system
(continues as Solaris -- see above).
UHC (80x86): pure SVR4, X11, Motif
Ultrix (DEC): based on 4.2BSD with much of 4.3.
Newsgroup: comp.unix.ultrix.
- 4.4 is latest
UNICOS (Cray): System V base. Newsgroup: comp.unix.cray
- 5.x, 6,x, 7.0
UnixWare Release 4.2 [Univel]: SVR4.2; over NetWare. Univel no longer
exists.
UTEK (Tektronix)
- 4.0
VOLVIX (Archipel S.A.): UNIX-based OS built around a communication
based, distributed, real-time micro-kernel. SVR3.2 system calls,
BSD4.4 file/network system calls (VFS, FFS). Also NFS and X11.
Vanilla VOLVIX is for transputers.
Xenix (80x86): 1st Unix on Intel hardware, based on SVR2 (previously on
S III and even V7). Newsgroup: comp.unix.xenix.
------------------------------
Subject: Real-time Unices.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Tue Aug 15 15:14:00 EDT 1995
X-Version: 2.9
WARNING: this section is badly in need of work. It's full of errors,
and it's incomplete. I hope to have time to look at it this winter
(was "this fall"). I doubt all of following are Unices -- input is
welcome. The list also includes more common Unices with real-time
features, and some non-Unix systems with Unix-like APIs. I don't
suppose the latter really belong here, but having collected some notes,
I'm hesitant to junk them. See also comp.realtime.
AIX: AIX/6000 has real-time support.
Concurrent OS (Concurrent): real Unix, significantly modifed by
Concurrent.
CX/UX: a real UNIX significantly modified by Harris to provide
real-time capabilities and performance. Compliant with POSIX.4 final
version.
EP/LX (Control Data): port of LynxOS to R3000. Formerly called TC/IX.
LynxOS (Lynx Real-Time Systems, Inc): Berkeley and SV compatibility,
ground-up rewrite (proprietary), predates SVR4. Is not UNIX, but
supports much of the UNIX I/Fs (SV and BSD). POSIX compliant. Fully
preemptive, fixed priorities.
MiX: microkernel implementation of SVR4 offered by Chorus.
Motorola SVR4 has real-time capabilities.
QNX (Quantum Software): unix-compatible real real-time OS.
REAL/IX: based on System V 3.2 with RT features (fully premptive kernel,
fixed-priority scheduler, RT timer, &c.). For 68xxx and 88xxx based
systems. POSIX (1003.1 - 1988) compliant and in 88k form, it is
88open BCS compliant. Also available for x86/Pentium.
RTMX O/S [RTMX Incorporated]: elements of NET2, 4.4BSD-Lite and
proprietary code. Also includes FSF tools. Real-time (POSIX)
extensions.
RTU (Concurrent), for 68K boxes
Solaris 2 has real-time capabilities?
Stellix (Stardent); it's Unix, but is it real-time?
Venix/386: Interactive SVR3.2 with real-time extensions.
VMEexec (Motorola): not Unix, but also shares some I/Fs with Unix.
VxWorks (Wind River Systems): Little in common with Unix, has some I/Fs
in common with Unix (but not the file system). Newsgroup:
comp.os.vxworks.
(know nothing about)
Convex RTS
REAL/IX (AEG)
Sorix (Siemens)
System V/86 (Motorola)
TC/IX (CCD)
Velocity (Ready Systems):
------------------------------
Subject: Unix glossary.
From: "Pierre (P.) Lewis" <lew@bnr.ca>
Date: Tue Aug 15 15:14:00 EDT 1995
X-Version: 2.9
This section provides short definitions of various concepts and
components of (or related to) Unix systems.
Chorus: message-passing microkernel, may form basis for a future release
of SV. Chorus already have SVR4 running on top (binary-compatible).
CORBA (Common Object Request Broker Architecture).
COSE (Common Open Software Environment) [Sun, HP, IBM]: common look and
feel (Motif -- Sun will let OpenLook fade away), common API.
Reaction against Windows NT. See section 6.4 above.
DCE (Distributed Computing Environment, from OSF): Includes RPC (Apollo's
NCS), directory service (local based on DNS, global on X.500), time,
security, and threads services, DFS (distrib. file system), ....
OS-independent.
DME (Distributed Management Environment, from OSF): future.
DO (Distributed Objects [Enterprise]): ???.
FFS (Fast File System): from Berkeley, 1983. Equivalent (exact?) of
UFS in SunOS. Has notions such as cylinder groups, fragments.
FSF (Free Software Foundation)
Mach: modern kernels from CMU (Carnegie Mellon University) on which many
Unices and other OSs are based (e.g. OSF/1, MacMach, ...):
- 2.5: monolithic kernel with 4.2BSD
- 3.0: microkernel with BSD Unix server in user space (and other OSs,
e.g. MS-DOS)
Newsgroup: comp.os.mach
MFS (Memory File System):
NeWS (Network extensible Window System), from Sun?: PostScript-based,
networked, toolkits (and even clients) loaded in server. Part of
OpenWindows.
NFS (Network File System): contributed by Sun to BSD, stateless server
ONC (Open Network Computing): from Sun(?), includes RPC, name service
(NIS aka YP), NFS, ... (found in many Unices, other OSs).
OpenStep [NeXT, Sun]: ???
PowerOpen: both a standard, and an organization promoting PowerPC.
Involves IBM, Apple and Motorola; others? See section 6.4 above.
PowerPC (PPC): a RISC CPU chip [IBM, Motorola].
RFS (Remote File System): SV, stateful server, incompatible with NFS
RPC (Remote Procedure Call): high-level IPC (inter-process communication)
mechanism. Two flavors.
- ONC: Over TCP or UDP (later OSI), uses XDR to encode data.
- DCE: has a different RPC mechanism (based on Apollo's NCS)
S5 FS: System V's native file system, blocks 512 to 2K.
sockets: BSD interface mechanism to networks (compare TLI).
STREAMS: a message-passing kernel mechanism, initially in SVR3, which
provides a very good interface for protocol development.
TFS (Translucent File System): Sun, COW applied to files.
TLI (Transport Library Interface): SV's interface to transport services
(TCP, OSI). UI has also defined an APLI (ACSE/Presentation Library
Interface)
UFS (?): BSD's native file system as seen in SunOS, blocks 4K to 8K,
cylinder groups, fragments.
XTI (X/Open Transport Interface): TLI with enhancements
X11: pixel-oriented window system from MIT.
------------------------------
Subject: RCS vs SCCS: Introduction
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
The majority of the replies (in a recent poll) were in favor of
RCS, a few for SCCS, and a few suggested alternatives such as CVS.
Functionally RCS and SCCS are practically equal, with RCS having
a bit more features since it continues to be updated.
Note that RCS learned from the mistakes of SCCS...
------------------------------
Subject: RCS vs SCCS: How do the interfaces compare?
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
RCS has an easier interface for first time users. There are less
commands, it is more intuitive and consistent, and it provides
more useful arguments.
Branches have to be specifically created in SCCS. In RCS, they
are checked in as any other version.
------------------------------
Subject: RCS vs SCCS: What's in a Revision File?
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
RCS keeps history in files with a ",v" suffix. SCCS keeps
history in files with a "s." prefix.
RCS looks for RCS files automatically in the current directory or
in a RCS subdirectory, or you can specify an alternate RCS file.
The sccs front end to SCCS always uses the SCCS directory. If
you don't use the sccs front end, you must specify the full SCCS
filename.
RCS stores its revisions by holding a copy of the latest version
and storing backward deltas. SCCS uses a "merged delta"
concept.
All RCS activity takes place within a single RCS file. SCCS
maintains several files. This can be messy and confusing.
Editing either RCS or SCCS files is a bad idea because mistakes
are so easy to make and so fatal to the history of the file.
Revision information is easy to edit in both types, whereas one
would not want to edit the actual text of a version in RCS. If
you edit an SCCS file, you will have to recalculate the checksum
using the admin program.
------------------------------
Subject: RCS vs SCCS: What are the keywords?
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
RCS and SCCS use different keywords that are expanded in the
text. For SCCS the keyword "%I%" is replaced with the revision
number if the file is checked out for reading.
The RCS keywords are easier to remember, but keyword expansion is
more easily customized in SCCS.
In SCCS, keywords are expanded on a read-only get. If a version
with expanded keywords is copied into a file that will be
deltaed, the keywords will be lost and the version information in
the file will not be updated. On the other hand, RCS retains the
keywords when they are expanded so this is avoided.
------------------------------
Subject: What's an RCS symbolic name?
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
RCS allows you treat a set of files as a family of files while
SCCS is meant primarily for keeping the revision history of
files.
RCS accomplishes that with symbolic names: you can mark all the
source files associated with an application version with `rcs
-n', and then easily retrieve them later as a cohesive unit. In
SCCS you would have to do this by writing a script to write or
read all file names and versions to or from a file.
------------------------------
Subject: RCS vs SCCS: How do they compare for performance?
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
Since RCS stores the latest version in full, it is much faster in
retrieving the latest version. After RCS version 5.6, it is also
faster than SCCS in retrieving older versions.
------------------------------
Subject: RCS vs SCCS: Version Identification.
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
SCCS is able to determine when a specific line of code was added
to a system.
------------------------------
Subject: RCS vs SCCS: How do they handle problems?
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
If you are missing the sccs or rcs tools, or the RCS or SCCS file
is corrupt and the tools don't work on it, you can still retrieve
the latest version in RCS. Not true with SCCS.
------------------------------
Subject: RCS vs SCCS: How do they interact with make(1)?
Date: Wed, 30 Dec 1992 10:41:51 -0700
From: Blair P. Houghton <bhoughto@sedona.intel.com>
The fact that SCCS uses prefixes (s.file.c) means that make(1)
can't treat them in an ordinary manner, and special rules
(involving '~' characters) must be used in order for make(1) to
work with SCCS; even so, make(1) on some UNIX platforms will not
apply default rules to files that are being managed with SCCS.
The suffix notation (file.c,v) for RCS means that ordinary
suffix-rules can be used in all implementations of make(1), even
if the implementation isn't designed to handle RCS files
specially.
------------------------------
Subject: RCS vs SCCS: Conversion.
Date: Tue, 10 Jan 1995 21:01:41 -0500
From: Ed Ravin <elr@wp.prodigy.com>
An unsupported C-Shell script is available to convert from SCCS
to RCS. You can find it in
ftp://ftp.std.com/src/gnu/cvs-1.3/contrib/sccs2rcs
One would have to write their own script or program to convert
from RCS to SCCS.
------------------------------
Subject: RCS vs SCCS: Support
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
SCCS is supported by AT&T. RCS is supported by the Free Software
Foundation. Therefore RCS runs on many more platforms, including
PCs.
Most make programs recognize SCCS's "s." prefix while GNU make
is one of the few that handles RCS's ",v" suffix.
Some tar programs have a -F option that ignores either RCS
directories, or SCCS directories or both.
------------------------------
Subject: RCS vs SCCS: Command Comparison
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
SCCS RCS Explanation
==== === ===========
sccs admin -i -nfile file ci file Checks in the file
for the first time,
creating the revision
history file.
sccs get file co file Check out a file for
reading.
sccs edit file co -l file Check out a file for
modification.
sccs delta file ci file Check in a file
previously locked.
what file ident file Print keyword
information.
sccs prs file rlog file Print a history of
the file.
sccs sccsdiff -rx -ry file rcsdiff -rx -ry file Compare two
revisions.
sccs diffs file rcsdiff file Compare current with
last revision.
sccs edit -ix-y file rcsmerge -rx-y file Merge changes between
two versions into
file.
??? rcs -l file Lock the latest
revision.
??? rcs -u file Unlock the latest
revision. Possible
to break another's
lock, but mail is
sent to the other
user explaining why.
------------------------------
Subject: RCS vs SCCS: Acknowledgements
Date: Sat, 10 Oct 92 19:34:39 +0200
From: Bill Wohler <wohler@newt.com>
I would like to thank the following persons for contributing to
these articles. I'd like to add your name to the list--please
send comments or more references to Bill Wohler <wohler@newt.com>.
Karl Vogel <vogel@c-17igp.wpafb.af.mil>
Mark Runyan <runyan@hpcuhc.cup.hp.com>
Paul Eggert <eggert@twinsun.com>
Greg Henderson <henders@infonode.ingr.com>
Dave Goldberg <dsg@mbunix.mitre.org>
Rob Kurver <rob@pact.nl>
Raymond Chen <rjc@math.princeton.edu>
Dwight <dwight@s1.gov>
------------------------------
Subject: Can I get more information on configuration management systems?
Date: Thu Oct 15 10:27:47 EDT 1992
From: Ted Timar <tmatimar@isgtec.com>
Bill Wohler, who compiled all of the information in this part of
the FAQ, has compiled much more information. This information is
available for ftp from ftp.wg.omron.co.jp (133.210.4.4) under
"pub/unix-faq/docs/rev-ctl-sys".
------------------------------
Questions and remarks can be send to: bass@uci.kun.nl<= Back to document root