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Chet Ramey
2011-12-07 09:05:53 -05:00
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@@ -1,18 +1,18 @@
From: chet@po.cwru.edu (Chet Ramey)
From: chet.ramey@case.edu (Chet Ramey)
To: bug-bash@gnu.org
Subject: BASH Frequently-Asked Questions (FAQ version 3.30)
Reply-To: chet@po.cwru.edu
Subject: BASH Frequently-Asked Questions (FAQ version 3.35)
Cc: chet.ramey@case.edu
Reply-To: chet.ramey@case.edu
Archive-name: unix-faq/shell/bash
Posting-Frequency: monthly
Submitted-By: chet@po.cwru.edu (Chet Ramey)
Last-Modified: Mon Feb 14 11:57:02 EST 2005
FAQ-Version: 3.30
Bash-Version: 3.0
Last-Modified: Thu Dec 14 11:34:54 EST 2006
FAQ-Version: 3.35
Bash-Version: 3.2
URL: ftp://ftp.cwru.edu/pub/bash/FAQ
Maintainer: chet@po.cwru.edu (Chet Ramey)
This is the Bash FAQ, version 3.30, for Bash version 3.0.
This is the Bash FAQ, version 3.35, for Bash version 3.2.
This document contains a set of frequently-asked questions concerning
Bash, the GNU Bourne-Again Shell. Bash is a freely-available command
@@ -23,7 +23,7 @@ Another good source of basic information about shells is the collection
of FAQ articles periodically posted to comp.unix.shell.
Questions and comments concerning this document should be sent to
chet@po.cwru.edu.
chet.ramey@case.edu.
This document is available for anonymous FTP with the URL
@@ -50,9 +50,9 @@ A10) What is the bash `posix mode'?
Section B: The latest version
B1) What's new in version 3.0?
B2) Are there any user-visible incompatibilities between bash-3.0 and
bash-1.14.7?
B1) What's new in version 3.2?
B2) Are there any user-visible incompatibilities between bash-3.2 and
bash-2.05b?
Section C: Differences from other Unix shells
@@ -92,6 +92,7 @@ E10) Why does `cd //' leave $PWD as `//'?
E11) If I resize my xterm while another program is running, why doesn't bash
notice the change?
E12) Why don't negative offsets in substring expansion work like I expect?
E13) Why does filename completion misbehave if a colon appears in the filename?
Section F: Things to watch out for on certain Unix versions
@@ -154,26 +155,26 @@ of Case Western Reserve University.
A2) What's the latest version?
The latest version is 3.0, first made available on 27 July, 2004.
The latest version is 3.2, first made available on 12 October, 2006.
A3) Where can I get it?
Bash is the GNU project's shell, and so is available from the
master GNU archive site, ftp.gnu.org, and its mirrors. The
latest version is also available for FTP from ftp.cwru.edu.
The following URLs tell how to get version 3.0:
The following URLs tell how to get version 3.2:
ftp://ftp.gnu.org/pub/gnu/bash/bash-3.0.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-3.0.tar.gz
ftp://ftp.gnu.org/pub/gnu/bash/bash-3.2.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-3.2.tar.gz
Formatted versions of the documentation are available with the URLs:
ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-3.0.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-doc-3.0.tar.gz
ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-3.2.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-doc-3.2.tar.gz
Any patches for the current version are available with the URL:
ftp://ftp.cwru.edu/pub/bash/bash-3.0-patches/
ftp://ftp.cwru.edu/pub/bash/bash-3.2-patches/
A4) On what machines will bash run?
@@ -204,10 +205,10 @@ of their CYGWIN project. For more information about the project, see
http://www.cygwin.com/.
Cygnus originally ported bash-1.14.7, and that port was part of their
early GNU-Win32 (the original name) releases. Cygnus has also done a
port of bash-2.05b to the CYGWIN environment, and it is available as
part of their current release. Bash-3.0 is currently being tested and
should be available soon.
early GNU-Win32 (the original name) releases. Cygnus has also done
ports of bash-2.05b and bash-3.0 to the CYGWIN environment, and both
are available as part of their current release. Bash-3.2 is currently
being tested and should be available soon.
Bash-2.05b and later versions should require no local Cygnus changes to
build and run under CYGWIN.
@@ -229,7 +230,8 @@ ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204s.zip source
Mark began to work with bash-2.05, but I don't know the current status.
Bash-3.0 compiles and runs with no modifications under Microsoft's Services
for Unix (SFU), once known as Interix.
for Unix (SFU), once known as Interix. I do not anticipate any problems
with building bash-3.1 or bash-3.2.
A6) How can I build bash with gcc?
@@ -398,15 +400,33 @@ They are also listed in a section in the Bash Reference Manual
Section B: The latest version
B1) What's new in version 3.0?
B1) What's new in version 3.2?
Bash-3.0 is the third major release of bash. The features introduced
in the intermediate releases following bash-2.05 have been completed.
Support for the bash debugger (a separate project) has been integrated.
Bash-3.2 is the second maintenance release of the third major release of
bash. It contains the following significant new features (see the manual
page for complete descriptions and the CHANGES and NEWS files in the
bash-3.2 distribution).
Bash-3.0 contains the following new features (see the manual page for
complete descriptions and the CHANGES and NEWS files in the bash-3.0
distribution):
o Bash-3.2 now checks shell scripts for NUL characters rather than non-printing
characters when deciding whether or not a script is a binary file.
o Quoting the string argument to the [[ command's =~ (regexp) operator now
forces string matching, as with the other pattern-matching operators.
A short feature history dating from Bash-2.0:
Bash-3.1 contained the following new features:
o Bash-3.1 may now be configured and built in a mode that enforces strict
POSIX compliance.
o The `+=' assignment operator, which appends to the value of a string or
array variable, has been implemented.
o It is now possible to ignore case when matching in contexts other than
filename generation using the new `nocasematch' shell option.
Bash-3.0 contained the following new features:
o Features to support the bash debugger have been implemented, and there
is a new `extdebug' option to turn the non-default options on
@@ -436,8 +456,6 @@ o The `jobs', `kill', and `wait' builtins now accept job control notation
o The `gettext' package and libintl have been integrated, and the shell
messages may be translated into other languages
A short feature history dating from Bash-2.0:
Bash-2.05b introduced the following new features:
o support for multibyte characters has been added to both bash and readline
@@ -645,10 +663,10 @@ grammar tighter and smaller (66 reduce-reduce conflicts gone)
lots of code now smaller and faster
test suite greatly expanded
B2) Are there any user-visible incompatibilities between bash-3.0 and
bash-1.14.7?
B2) Are there any user-visible incompatibilities between bash-3.2 and
bash-2.05b?
There are a few incompatibilities between version 1.14.7 and version 3.0.
There are a few incompatibilities between version 2.05b and version 3.2.
They are detailed in the file COMPAT in the bash distribution. That file
is not meant to be all-encompassing; send mail to bash-maintainers@gnu.org
if if you find something that's not mentioned there.
@@ -702,7 +720,7 @@ Things bash has that sh does not:
read -e/-p/-a/-t/-n/-d/-s/-u,
readonly -a/-f/name=value, trap -l, set +o,
set -b/-m/-o option/-h/-p/-B/-C/-H/-P,
unset -f/-v, ulimit -m/-p/-u,
unset -f/-v, ulimit -i/-m/-p/-q/-u/-x,
type -a/-p/-t/-f/-P, suspend -f, kill -n,
test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S
bash reads ~/.bashrc for interactive shells, $ENV for non-interactive
@@ -731,11 +749,12 @@ Things bash has that sh does not:
case-insensitive pattern matching and globbing
variable assignments preceding commands affect only that command,
even for builtins and functions
posix mode
posix mode and strict posix conformance
redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr,
/dev/tcp/host/port, /dev/udp/host/port
debugger support, including `caller' builtin and new variables
RETURN trap
the `+=' assignment operator
Things sh has that bash does not:
@@ -797,8 +816,8 @@ Things bash has or uses that ksh88 does not:
set -o braceexpand/-o histexpand/-o interactive-comments/
-o notify/-o physical/-o posix/-o hashall/-o onecmd/
-h/-B/-C/-b/-H/-P, set +o, suspend, trap -l, type,
typeset -a/-F/-p, ulimit -u, umask -S, alias -p, shopt,
disown, printf, complete, compgen
typeset -a/-F/-p, ulimit -i/-q/-u/-x, umask -S, alias -p,
shopt, disown, printf, complete, compgen
`!' csh-style history expansion
POSIX.2-style globbing character classes
POSIX.2-style globbing equivalence classes
@@ -813,6 +832,7 @@ Things bash has or uses that ksh88 does not:
RETURN trap
Timestamps in history entries
{x..y} brace expansion
The `+=' assignment operator
Things ksh88 has or uses that bash does not:
tracked aliases (alias -t)
@@ -840,7 +860,7 @@ Implementation differences:
C3) Which new features in ksh-93 are not in bash, and which are?
New things in ksh-93 not in bash-3.0:
New things in ksh-93 not in bash-3.2:
associative arrays
floating point arithmetic and variables
math library functions
@@ -859,7 +879,6 @@ New things in ksh-93 not in bash-3.0:
`fc' has been renamed to `hist'
`.' can execute shell functions
exit statuses between 0 and 255
`+=' variable assignment operator
FPATH and PATH mixing
getopts -a
-I invocation option
@@ -867,7 +886,7 @@ New things in ksh-93 not in bash-3.0:
lexical scoping for local variables in `ksh' functions
no scoping for local variables in `POSIX' functions
New things in ksh-93 present in bash-3.0:
New things in ksh-93 present in bash-3.2:
[n]<&word- and [n]>&word- redirections (combination dup and close)
for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command
?:, ++, --, `expr1 , expr2' arithmetic operators
@@ -893,6 +912,7 @@ New things in ksh-93 present in bash-3.0:
command name completion
ENV processed only for interactive shells
set -o pipefail
The `+=' assignment operator
Section D: Why does bash do some things differently than other Unix shells?
@@ -1116,9 +1136,8 @@ will try to write on a pipe without a reader. In that case, bash
will print `Broken pipe' to stderr when ps is killed by a
SIGPIPE.
You can build a version of bash that will not report SIGPIPE errors
by uncommenting the definition of DONT_REPORT_SIGPIPE in the file
config-top.h.
As of bash-3.1, bash does not report SIGPIPE errors by default. You
can build a version of bash that will report such errors.
E3) When I have terminal escape sequences in my prompt, why does bash
wrap lines at the wrong column?
@@ -1145,12 +1164,12 @@ simple calls to `read'. For example, piping a command's output
into a `while' loop that repeatedly calls `read' will result in
the same behavior.
Each element of a pipeline runs in a separate process, a child of
the shell running the pipeline. A subprocess cannot affect its
parent's environment. When the `read' command sets the variable
to the input, that variable is set only in the subshell, not the
parent shell. When the subshell exits, the value of the variable
is lost.
Each element of a pipeline, even a builtin or shell function,
runs in a separate process, a child of the shell running the
pipeline. A subprocess cannot affect its parent's environment.
When the `read' command sets the variable to the input, that
variable is set only in the subshell, not the parent shell. When
the subshell exits, the value of the variable is lost.
Many pipelines that end with `read variable' can be converted
into command substitutions, which will capture the output of
@@ -1394,6 +1413,32 @@ expanded value of param is unset or null, and $param otherwise.
To use negative offsets that begin with a minus sign, separate the
minus sign and the colon with a space.
E13) Why does filename completion misbehave if a colon appears in the filename?
Filename completion (and word completion in general) may appear to behave
improperly if there is a colon in the word to be completed.
The colon is special to readline's word completion code: it is one of the
characters that breaks words for the completer. Readline uses these characters
in sort of the same way that bash uses $IFS: they break or separate the words
the completion code hands to the application-specific or default word
completion functions. The original intent was to make it easy to edit
colon-separated lists (such as $PATH in bash) in various applications using
readline for input.
This is complicated by the fact that some versions of the popular
`bash-completion' programmable completion package have problems with the
default completion behavior in the presence of colons.
The current set of completion word break characters is available in bash as
the value of the COMP_WORDBREAKS variable. Removing `:' from that value is
enough to make the colon not special to completion:
COMP_WORDBREAKS=${COMP_WORDBREAKS//:}
You can also quote the colon with a backslash to achieve the same result
temporarily.
Section F: Things to watch out for on certain Unix versions
F1) Why can't I use command line editing in my `cmdtool'?
@@ -1579,6 +1624,9 @@ this. These variables can be set in your .inputrc or using the bash
The `set' commands between the single quotes may also be placed
in ~/.inputrc.
The script examples/scripts.noah/meta.bash encapsulates the bind
commands in a shell function.
G2) How do I write a function `x' to replace builtin command `x', but
still invoke the command from within the function?
@@ -1752,20 +1800,26 @@ ftp.cwru.edu in the `pub/bash' directory.
Cameron Newham and Bill Rosenblatt have written a book on bash, published
by O'Reilly and Associates. The book is based on Bill Rosenblatt's Korn
Shell book. The title is ``Learning the Bash Shell'', and the ISBN number
is 1-56592-147-X. Look for it in fine bookstores near you. This book
covers bash-1.14, but has an appendix describing some of the new features
in bash-2.0.
A second edition of this book is available, published in January, 1998.
The ISBN number is 1-56592-347-2. Look for it in the same fine bookstores
or on the web.
of the third edition, published in March, 2005, is 0-596-00965-8. Look for
it in fine bookstores near you. This edition of the book has been updated
to cover bash-3.0.
The GNU Bash Reference Manual has been published as a printed book by
Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Feb 2003). It covers
bash-2.0 and is available from most online bookstores (see
Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Nov. 2006). It covers
bash-3.2 and is available from most online bookstores (see
http://www.network-theory.co.uk/bash/manual/ for details). The publisher
will donate $1 to the Free Software Foundation for each copy sold.
Arnold Robbins and Nelson Beebe have written ``Classic Shell Scripting'',
published by O'Reilly. The first edition, with ISBN number 0-596-00595-4,
was published in May, 2005.
Chris F. A. Johnson, a frequent contributor to comp.unix.shell and
gnu.bash.bug, has written ``Shell Scripting Recipes: A Problem-Solution
Approach,'' a new book on shell scripting, concentrating on features of
the POSIX standard helpful to shell script writers. The first edition from
Apress, with ISBN number 1-59059-471-1, was published in May, 2005.
H3) What's coming in future versions?
These are features I hope to include in a future version of bash.
@@ -1784,16 +1838,15 @@ a bash programmer's guide with a chapter on creating loadable builtins
a better loadable interface to perl with access to the shell builtins and
variables (contributions gratefully accepted)
ksh93-like `nameref' variables
ksh93-like `+=' variable assignment operator
ksh93-like `xx.yy' variables (including some of the .sh.* variables) and
associated disipline functions
Some of the new ksh93 pattern matching operators, like backreferencing
H5) When will the next release appear?
The next version will appear sometime in 2005. Never make predictions.
The next version will appear sometime in 2007. Never make predictions.
This document is Copyright 1995-2004 by Chester Ramey.
This document is Copyright 1995-2006 by Chester Ramey.
Permission is hereby granted, without written agreement and
without license or royalty fees, to use, copy, and distribute