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@ -1,4 +1,4 @@
This is the Bash FAQ, version 3.17, for Bash version 2.05a.
This is the Bash FAQ, version 3.20, for Bash version 2.05b.
This document contains a set of frequently-asked questions concerning
Bash, the GNU Bourne-Again Shell. Bash is a freely-available command
@ -36,8 +36,8 @@ A10) What is the bash `posix mode'?
Section B: The latest version
B1) What's new in version 2.05a?
B2) Are there any user-visible incompatibilities between bash-2.05a and
B1) What's new in version 2.05b?
B2) Are there any user-visible incompatibilities between bash-2.05b and
bash-1.14.7?
Section C: Differences from other Unix shells
@ -74,6 +74,7 @@ E7) What about empty for loops in Makefiles?
E8) Why does the arithmetic evaluation code complain about `08'?
E9) Why does the pattern matching expression [A-Z]* match files beginning
with every letter except `z'?
E10) Why does `cd //' leave $PWD as `//'?
Section F: Things to watch out for on certain Unix versions
@ -86,6 +87,8 @@ F4) I'm running SVR4.2. Why is the line erased every time I type `@'?
F5) Why does bash report syntax errors when my C News scripts use a
redirection before a subshell command?
F6) Why can't I use vi-mode editing on Red Hat Linux 6.1?
F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on
HP/UX 11.x?
Section G: How can I get bash to do certain common things?
@ -134,23 +137,23 @@ of Case Western Reserve University.
A2) What's the latest version?
The latest version is 2.05a, first made available on Thursday, 15
November, 2001.
The latest version is 2.05b, first made available on Wednesday, 17
July, 2002.
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 2.05a:
The following URLs tell how to get version 2.05b:
ftp://ftp.gnu.org/pub/gnu/bash/bash-2.05a.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-2.05a.tar.gz
ftp://ftp.gnu.org/pub/gnu/bash/bash-2.05b.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-2.05b.tar.gz
Formatted versions of the documentation are available with the URLs:
ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-2.05a.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-doc-2.05a.tar.gz
ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-2.05b.tar.gz
ftp://ftp.cwru.edu/pub/bash/bash-doc-2.05b.tar.gz
A4) On what machines will bash run?
@ -187,7 +190,7 @@ early GNU-Win32 (the original name) releases. Cygnus has also done a
port of bash-2.05 to the CYGWIN environment, and it is available as
part of their current release.
Bash-2.05a should require no local Cygnus changes to build and run under
Bash-2.05b should require no local Cygnus changes to build and run under
CYGWIN.
The Cygnus port works only on Intel machines. There is a port of bash
@ -363,6 +366,10 @@ available on the web at
http://www.opengroup.org/onlinepubs/007908799/
The Single Unix Specification, version 3, is available on the web at
http://www.opengroup.org/onlinepubs/007904975/
A10) What is the bash `posix mode'?
Although bash is an implementation of the POSIX.2 shell
@ -370,29 +377,61 @@ specification, there are areas where the bash default behavior
differs from that spec. The bash `posix mode' changes the bash
behavior in these areas so that it obeys the spec more closely.
Posix mode is entered by starting bash with the --posix option or
executing `set -o posix' after bash is running.
Posix mode is entered by starting bash with the --posix or
'-o posix' option or executing `set -o posix' after bash is running.
The specific aspects of bash which change when posix mode is
active are listed in the file CWRU/POSIX.NOTES in the bash
distribution. They are also listed in a section in the Bash
Reference Manual.
active are listed in the file POSIX in the bash distribution.
They are also listed in a section in the Bash Reference Manual
(from which that file is generated).
Section B: The latest version
B1) What's new in version 2.05a?
B1) What's new in version 2.05b?
The raison d'etre for bash-2.05a is to make an intermediate release
containing principally bug fixes (some very good work was done and
contributed after bash-2.05 was released) available before I start to
work on the major new features to be available in the next release
(bash-2.06 or bash-3.0 or whatever I tag it). As such, there are
only a few relatively minor new features.
The raison d'etre for bash-2.05b is to make a second intermediate
release containing the first of the new features to be available
in bash-3.0 and get feedback on those features before proceeding.
The major new feature is multibyte character support in both Bash
and Readline.
Bash-2.05a contains the following new features (see the manual page for
complete descriptions and the CHANGES and NEWS files in the bash-2.05a
Bash-2.05b contains the following new features (see the manual page for
complete descriptions and the CHANGES and NEWS files in the bash-2.05b
distribution):
o support for multibyte characters has been added to both bash and readline
o the DEBUG trap is now run *before* simple commands, ((...)) commands,
[[...]] conditional commands, and for ((...)) loops
o the shell now performs arithmetic in the largest integer size the machine
supports (intmax_t)
o there is a new \D{...} prompt expansion; passes the `...' to strftime(3)
and inserts the result into the expanded prompt
o there is a new `here-string' redirection operator: <<< word
o when displaying variables, function attributes and definitions are shown
separately, allowing them to be re-used as input (attempting to re-use
the old output would result in syntax errors).
o `read' has a new `-u fd' option to read from a specified file descriptor
o the bash debugger in examples/bashdb has been modified to work with the
new DEBUG trap semantics, the command set has been made more gdb-like,
and the changes to $LINENO make debugging functions work better
o the expansion of $LINENO inside a shell function is only relative to the
function start if the shell is interactive -- if the shell is running a
script, $LINENO expands to the line number in the script. This is as
POSIX-2001 requires
A short feature history dating from Bash-2.0:
Bash-2.05a introduced the following new features:
o The `printf' builtin has undergone major work
o There is a new read-only `shopt' option: login_shell, which is set by
@ -418,8 +457,6 @@ o Readline can be configured to place the user at the same point on the line
o Readline can be configured to skip `hidden' files (filenames with a leading
`.' on Unix) when performing completion
A short feature history dating from bash-2.0:
Bash-2.05 introduced the following new features:
o This version has once again reverted to using locales and strcoll(3) when
@ -570,13 +607,13 @@ 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-2.05a and
B2) Are there any user-visible incompatibilities between bash-2.05b and
bash-1.14.7?
There are a few incompatibilities between version 1.14.7 and version 2.05a.
They are detailed in the file COMPAT in the bash-2.05a distribution. That
file is not meant to be all-encompassing; send mail to bash-maintainers@gnu.org
if you find something that's not mentioned there.
There are a few incompatibilities between version 1.14.7 and version 2.05b.
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.
Section C: Differences from other Unix shells
@ -589,6 +626,7 @@ completely.
Things bash has that sh does not:
long invocation options
[+-]O invocation option
-l invocation option
`!' reserved word to invert pipeline return value
`time' reserved word to time pipelines and shell builtins
the `function' reserved word
@ -601,7 +639,7 @@ Things bash has that sh does not:
the ${#param} parameter value length operator
the ${!param} indirect parameter expansion operator
the ${!param*} prefix expansion operator
the ${param:length[:offset]} parameter substring operator
the ${param:offset[:length]} parameter substring operator
the ${param/pat[/string]} parameter pattern substitution operator
expansions to perform substring removal (${p%[%]w}, ${p#[#]w})
expansion of positional parameters beyond $9 with ${num}
@ -616,18 +654,18 @@ Things bash has that sh does not:
DEBUG trap
ERR trap
variable arrays with new compound assignment syntax
redirections: <>, &>, >|
redirections: <>, &>, >|, <<<, [n]<&word-, [n]>&word-
prompt string special char translation and variable expansion
auto-export of variables in initial environment
command search finds functions before builtins
bash return builtin will exit a file sourced with `.'
builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -p/-t.
builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -d/-l/-p/-t.
export -n/-f/-p/name=value, pwd -L/-P,
read -e/-p/-a/-t/-n/-d/-s,
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,
type -a/-p/-t, suspend -f, kill -n,
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
bash restricted shell mode is more extensive
@ -690,15 +728,17 @@ C2) How does bash differ from the Korn shell, version ksh88?
Things bash has or uses that ksh88 does not:
long invocation options
[-+]O invocation option
-l invocation option
`!' reserved word
arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done
arithmetic in largest machine-supported size (intmax_t)
posix mode and posix conformance
command hashing
tilde expansion for assignment statements that look like $PATH
process substitution with named pipes if /dev/fd is not available
the ${!param} indirect parameter expansion operator
the ${!param*} prefix expansion operator
the ${param:length[:offset]} parameter substring operator
the ${param:offset[:length]} parameter substring operator
the ${param/pat[/string]} parameter pattern substitution operator
variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, SHLVL,
TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE,
@ -707,7 +747,7 @@ Things bash has or uses that ksh88 does not:
PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE,
GROUPS, FUNCNAME, histchars, auto_resume
prompt expansion with backslash escapes and command substitution
redirection: &> (stdout and stderr)
redirection: &> (stdout and stderr), <<<, [n]<&word-, [n]>&word-
more extensive and extensible editing and programmable completion
builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable,
exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history,
@ -727,6 +767,7 @@ Things bash has or uses that ksh88 does not:
`**' arithmetic operator to do exponentiation
redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr
arrays of unlimited size
TMOUT is default timeout for `read' and `select'
Things ksh88 has or uses that bash does not:
tracked aliases (alias -t)
@ -736,7 +777,7 @@ Things ksh88 has or uses that bash does not:
typeset +f to list all function names without definitions
text of command history kept in a file, not memory
builtins: alias -x, cd old new, fc -e -, newgrp, print,
read -p/-s/-u/var?prompt, set -A/-o gmacs/
read -p/-s/var?prompt, set -A/-o gmacs/
-o bgnice/-o markdirs/-o nolog/-o trackall/-o viraw/-s,
typeset -H/-L/-R/-Z/-A/-ft/-fu/-fx/-l/-u/-t, whence
using environment to pass attributes of exported variables
@ -754,7 +795,7 @@ Implementation differences:
C3) Which new features in ksh-93 are not in bash, and which are?
New things in ksh-93 not in bash-2.05a:
New things in ksh-93 not in bash-2.05b:
associative arrays
floating point arithmetic and variables
math library functions
@ -775,15 +816,14 @@ New things in ksh-93 not in bash-2.05a:
exit statuses between 0 and 255
set -o pipefail
`+=' variable assignment operator
TMOUT is default timeout for `read' and `select'
<&N- and >&N- redirections (combination dup and close)
FPATH and PATH mixing
getopts -a
-I invocation option
DEBUG trap now executed before each simple command, instead of after
printf %H, %P, %T, %Z modifiers, output base for %d
New things in ksh-93 present in bash-2.05a:
New things in ksh-93 present in bash-2.05b:
[n]<&word- and [n]>&word- redirections (combination dup and close)
for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command
?:, ++, --, `expr1 , expr2' arithmetic operators
expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]},
@ -980,7 +1020,7 @@ ksh-93 feature Bash equivalent
sleep, getconf Bash has loadable versions in examples/loadables
${.sh.version} $BASH_VERSION
print -f printf
hist alias fc=hist
hist alias hist=fc
$HISTEDIT $FCEDIT
Section E: How can I get bash to do certain things, and why does bash do
@ -1139,7 +1179,7 @@ configure with the --enable-xpg-echo-default option to turn this
on. Be aware that this will cause some of the tests run when you
type `make tests' to fail.
There is a shell option, `xpg_echo', settable with `shopt' that will
There is a shell option, `xpg_echo', settable with `shopt', that will
change the behavior of echo at runtime. Enabling this option turns
on expansion of backslash-escape sequences.
@ -1215,10 +1255,9 @@ http://www.pasc.org/interps/unofficial/db/p1003.2/pasc-1003.2-173.html
E9) Why does the pattern matching expression [A-Z]* match files beginning
with every letter except `z'?
Bash-2.05 and later versions have reverted to the bash-2.03 behavior of
honoring the current locale setting when processing ranges within pattern
matching bracket expressions ([A-Z]). This is what POSIX.2 and SUSv2/XPG5
specify.
Bash-2.03, Bash-2.05 and later versions honor the current locale setting
when processing ranges within pattern matching bracket expressions ([A-Z]).
This is what POSIX.2 and SUSv3/XPG6 specify.
The behavior of the matcher in bash-2.05 and later versions depends on the
current LC_COLLATE setting. Setting this variable to `C' or `POSIX' will
@ -1229,7 +1268,11 @@ this:
AaBb...Zz
which means that [A-Z] matches every letter except `z'.
which means that [A-Z] matches every letter except `z'. Others collate like
aAbBcC...zZ
which means that [A-Z] matches every letter except `a'.
The portable way to specify upper case letters is [:upper:] instead of
A-Z; lower case may be specified as [:lower:] instead of a-z.
@ -1252,6 +1295,16 @@ from removing every file in the current directory except those beginning
with `z' and still allow individual users to change the collation order.
Users may put the above command into their own profiles as well, of course.
E10) Why does `cd //' leave $PWD as `//'?
POSIX.2, in its description of `cd', says that *three* or more leading
slashes may be replaced with a single slash when canonicalizing the
current working directory.
This is, I presume, for historical compatibility. Certain versions of
Unix, and early network file systems, used paths of the form
//hostname/path to access `path' on server `hostname'.
Section F: Things to watch out for on certain Unix versions
F1) Why can't I use command line editing in my `cmdtool'?
@ -1386,6 +1439,21 @@ to the beginning of /etc/inputrc, or bracket the key bindings in
[...]
$endif
F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on
HP/UX 11.x?
HP/UX's support for long double is imperfect at best.
GCC will support it without problems, but the HP C library functions
like strtold(3) and printf(3) don't actually work with long doubles.
HP implemented a `long_double' type as a 4-element array of 32-bit
ints, and that is what the library functions use. The ANSI C
`long double' type is a 128-bit floating point scalar.
The easiest fix, until HP fixes things up, is to edit the generated
config.h and #undef the HAVE_LONG_DOUBLE line. After doing that,
the compilation should complete successfully.
Section G: How can I get bash to do certain common things?
G1) How can I get bash to read and display eight-bit characters?
@ -1607,11 +1675,8 @@ H3) What's coming in future versions?
These are features I hope to include in a future version of bash.
a better bash debugger (a minimally-tested version is included with bash-2.05a)
a better bash debugger (a minimally-tested version is included with bash-2.05b)
associative arrays
changes to the DEBUG trap to be compatible with ksh93 (which runs the
trap before each simple command, instead of after each one like previous
versions)
co-processes, but with a new-style syntax that looks like function declaration
H4) What's on the bash `wish list' for future versions?
@ -1621,7 +1686,6 @@ These are features that may or may not appear in a future version of bash.
breaking some of the shell functionality into embeddable libraries
a module system like zsh's, using dynamic loading like builtins
better internationalization using GNU `gettext'
an option to use external files for the long `help' text
date-stamped command history
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
@ -1637,7 +1701,7 @@ H5) When will the next release appear?
The next version will appear sometime in 2002. Never make predictions.
This document is Copyright 1995-2001 by Chester Ramey.
This document is Copyright 1995-2002 by Chester Ramey.
Permission is hereby granted, without written agreement and
without license or royalty fees, to use, copy, and distribute