Unix shell - View topic - Unix - Frequently Asked Questions (Contents) [Frequent posting]

Ted Tim
#16 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/contents
Version: $Id: contents,v 2.9 1996/06/11 13:08:13 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
tmati...@isgtec.com.

--
Ted Timar - tmati...@isgtec.com
ISG Technologies Inc., 6509 Airport Road, Mississauga, Ontario, Canada L4V 1S7

Tue, 19 Sep 2006 20:26:21 GMT

Ted Tim
#17 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/part1
Version: $Id: part1,v 2.9 1996/06/11 13:07:56 tmatimar Exp $

These 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).

This article includes answers to:

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?

If you're looking for the answer to, say, question 1.5, and want to skip
everything else, you can search ahead for the regular expression "^1.5)".

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
tmati...@isgtec.com.

----------------------------------------------------------------------

Subject: Who helped you put this list together?
Date: Thu Mar 18 17:16:55 EST 1993

1.1) Who helped you put this list together?

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 <wi...@dcdmjw.fnal.gov>.

Part 6 of this document (Unix flavours) was written almost entirely by
Pierre (P.) Lewis <l...@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 <leis...@sdsp.mc.xerox.com> cleaned up the Texinfo
version.

Major contributors to this document who may or may not be
recognized elsewhere are:

Steve Hayman <shay...@Objectario.com>
Pierre Lewis <l...@bnr.ca>
Jonathan Kamens <j...@mit.edu>
Tom Christiansen <tchr...@mox.perl.com>
Maarten Litmaath <ma...@nat.vu.nl>
Guy Harris <g...@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

1.2) When someone refers to 'rn(1)' or 'ctime(3)', what does
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

1.3) What does {some strange unix command name} stand for?

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
...

read more »

Tue, 19 Sep 2006 20:26:21 GMT

Ted Tim
#18 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/part3
Version: $Id: part3,v 2.9 1996/06/11 13:07:56 tmatimar Exp $

These 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).

This article includes answers to:

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 #! ... ?

If you're looking for the answer to, say, question 3.5, and want to skip
everything else, you can search ahead for the regular expression "^3.5)".

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
tmati...@isgtec.com.

----------------------------------------------------------------------

Subject: How do I find the creation time of a file?
Date: Thu Mar 18 17:16:55 EST 1993

3.1) How do I find the creation time of a file?

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

3.2) How do I use "rsh" without having the rsh hang around until the
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

3.3) How do I truncate a file?

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 <spen...@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
kucha...@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 ...

read more »

Tue, 19 Sep 2006 20:26:22 GMT

Ted Tim
#19 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/part4
Version: $Id: part4,v 2.9 1996/06/11 13:07:56 tmatimar Exp $

These 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).

This article includes answers to:

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?

If you're looking for the answer to, say, question 4.5, and want to skip
everything else, you can search ahead for the regular expression "^4.5)".

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
tmati...@isgtec.com.

----------------------------------------------------------------------

Subject: How do I read characters ... without requiring the user to hit RETURN?
Date: Thu Mar 18 17:16:55 EST 1993

4.1) How do I read characters from a terminal without requiring the user
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

4.2) How do I check to see if there are characters to be read without
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

4.3) How do I find the name of an open file?

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

4.4) How can an executing program determine its own pathname?

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

4.5) How do I use popen() to open a process for reading AND writing?

The problem with trying to pipe both input and output to an
arbitrary slave process is
...

read more »

Tue, 19 Sep 2006 20:26:23 GMT

Ted Tim
#20 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/part2
Version: $Id: part2,v 2.9 1996/06/11 13:07:56 tmatimar Exp $

These 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).

This article includes answers to:

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?

If you're looking for the answer to, say, question 2.5, and want to skip
everything else, you can search ahead 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
tmati...@isgtec.com.

----------------------------------------------------------------------

Subject: How do I remove a file whose name begins with a "-" ?
Date: Thu Mar 18 17:16:55 EST 1993

2.1) How do I remove a file whose name begins with a "-" ?

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

2.2) How do I remove a file with funny characters in the filename ?

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"
...

read more »

Tue, 19 Sep 2006 20:26:22 GMT

Ted Tim
#21 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/part5
Version: $Id: part5,v 2.9 1996/06/11 13:07:56 tmatimar Exp $

These 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).

This article includes answers to:

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?

If you're looking for the answer to, say, question 5.5, and want to skip
everything else, you can search ahead for the regular expression "^5.5)".

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
tmati...@isgtec.com.

----------------------------------------------------------------------

Subject: Can shells be classified into categories?
Date: Wed, 7 Oct 92 14:28:18 -0500

5.1) Can shells be classified into categories?

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?
Date: Wed, 7 Oct 92 14:28:18 -0500

5.2) How do I "include" one shell script from within another shell script?

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?
Date: Wed, 7 Oct 92 14:28:18 -0500

5.3) Do all shells have aliases? Is there something else that can be used?

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?
Date: Wed, 7 Oct 92 14:28:18 -0500

5.4) How are shell variables assigned?

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?
Date: Fri, 23 Oct 92 11:59:19 -0600

5.5) How can I tell if I am running an interactive shell?

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?
Date: Wed, 28 Oct 92 03:30:36 +0100

5.6) What "dot" files do the various shells use?

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 ... ?
...

read more »

Tue, 19 Sep 2006 20:26:23 GMT

Ted Tim
#22 / 16

Unix - Frequently Asked Questions (Contents) [Frequent posting]

Archive-name: unix-faq/faq/part6
Version: $Id: part6,v 2.9 1996/06/11 13:07:56 tmatimar Exp $

These 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).

This article includes answers to:

6.1) Disclaimer, introduction and acknowledgements.
6.2) A very brief look at Unix history.
6.3) Main Unix flavors.
6.4) 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.

If you're looking for the answer to, say, question 6.5, and want to skip
everything else, you can search ahead for the regular expression "^6.5)".

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
tmati...@isgtec.com.

----------------------------------------------------------------------

Subject: Disclaimer, introduction and acknowledgements.
Date: Tue Aug 15 15:14:00 EDT 1995
X-Version: 2.9

6.1) Disclaimer, introduction and acknowledgements.

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: l...@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: l...@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): p...@bnr.ca,
g...@auspex.com, p...@lysator.liu.se, mi...@ingres.com,
m...@saul.cis.upenn.edu, root%candle.u...@ls.com, e...@atbull.bull.co.at,
Aaron_Dai...@stortek.com, ra...@dci.pinetree.org, sb...@mcshh.hanse.de,
macm...@andrew.cmu.edu, j...@alw.nih.gov [4.4BSD], roe...@axpvms.cern.ch,
b...@pta.pyramid.com.au, b...@flatlin.ka.sub.org, m...@vail.tivoli.com,
d...@fch.wimsey.bc.ca, jlbr...@uswnvg.com, jpa...@usl.com,
y...@satelnet.org, merr...@gendev.slc.paramax.com, quin...@yggdrasil.com,
st...@rudolph.ssd.csd.harris.com, b...@heinous.isca.uiowa.edu,
p...@umich.edu, quin...@yggdrasil.com, Dan_Mench...@quickmail.apple.com,
D.Lamp...@sheffield.ac.uk, der...@vw.ece.cmu.edu, gor...@PowerOpen.org,
rom...@pyramid.com, r...@dain.oso.chalmers.se, c...@adi.com,
t...@tci002.uibk.ac.at, slle...@nando.net, ed...@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.
Date: Mon May 30 15:44:28 EDT 1994
X-Version: 2.6

6.2) A very brief look at Unix history.

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
...

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