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@@ -0,0 +1,2199 @@ +This is the Bash FAQ, version 4.11, for Bash version 4.1. + +This document contains a set of frequently-asked questions concerning +Bash, the GNU Bourne-Again Shell. Bash is a freely-available command +interpreter with advanced features for both interactive use and shell +programming. + +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.ramey@case.edu. + +This document is available for anonymous FTP with the URL + +ftp://ftp.cwru.edu/pub/bash/FAQ + +The Bash home page is http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html + +---------- +Contents: + +Section A: The Basics + +A1) What is it? +A2) What's the latest version? +A3) Where can I get it? +A4) On what machines will bash run? +A5) Will bash run on operating systems other than Unix? +A6) How can I build bash with gcc? +A7) How can I make bash my login shell? +A8) I just changed my login shell to bash, and now I can't FTP into my + machine. Why not? +A9) What's the `POSIX Shell and Utilities standard'? +A10) What is the bash `posix mode'? + +Section B: The latest version + +B1) What's new in version 4.1? +B2) Are there any user-visible incompatibilities between bash-4.1 and + previous bash versions? + +Section C: Differences from other Unix shells + +C1) How does bash differ from sh, the Bourne shell? +C2) How does bash differ from the Korn shell, version ksh88? +C3) Which new features in ksh-93 are not in bash, and which are? + +Section D: Why does bash do some things differently than other Unix shells? + +D1) Why does bash run a different version of `command' than + `which command' says it will? +D2) Why doesn't bash treat brace expansions exactly like csh? +D3) Why doesn't bash have csh variable modifiers? +D4) How can I make my csh aliases work when I convert to bash? +D5) How can I pipe standard output and standard error from one command to + another, like csh does with `|&'? +D6) Now that I've converted from ksh to bash, are there equivalents to + ksh features like autoloaded functions and the `whence' command? + +Section E: Why does bash do certain things the way it does? + +E1) Why is the bash builtin `test' slightly different from /bin/test? +E2) Why does bash sometimes say `Broken pipe'? +E3) When I have terminal escape sequences in my prompt, why does bash + wrap lines at the wrong column? +E4) If I pipe the output of a command into `read variable', why doesn't + the output show up in $variable when the read command finishes? +E5) I have a bunch of shell scripts that use backslash-escaped characters + in arguments to `echo'. Bash doesn't interpret these characters. Why + not, and how can I make it understand them? +E6) Why doesn't a while or for loop get suspended when I type ^Z? +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 `//'? +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? +E14) Why does quoting the pattern argument to the regular expression matching + conditional operator (=~) cause matching to stop working? +E15) Tell me more about the shell compatibility level. + +Section F: Things to watch out for on certain Unix versions + +F1) Why can't I use command line editing in my `cmdtool'? +F2) I built bash on Solaris 2. Why do globbing expansions and filename + completion chop off the first few characters of each filename? +F3) Why does bash dump core after I interrupt username completion or + `~user' tilde expansion on a machine running NIS? +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? + +G1) How can I get bash to read and display eight-bit characters? +G2) How do I write a function `x' to replace builtin command `x', but + still invoke the command from within the function? +G3) How can I find the value of a shell variable whose name is the value + of another shell variable? +G4) How can I make the bash `time' reserved word print timing output that + looks like the output from my system's /usr/bin/time? +G5) How do I get the current directory into my prompt? +G6) How can I rename "*.foo" to "*.bar"? +G7) How can I translate a filename from uppercase to lowercase? +G8) How can I write a filename expansion (globbing) pattern that will match + all files in the current directory except "." and ".."? + +Section H: Where do I go from here? + +H1) How do I report bugs in bash, and where should I look for fixes and + advice? +H2) What kind of bash documentation is there? +H3) What's coming in future versions? +H4) What's on the bash `wish list'? +H5) When will the next release appear? + +---------- +Section A: The Basics + +A1) What is it? + +Bash is a Unix command interpreter (shell). It is an implementation of +the Posix 1003.2 shell standard, and resembles the Korn and System V +shells. + +Bash contains a number of enhancements over those shells, both +for interactive use and shell programming. Features geared +toward interactive use include command line editing, command +history, job control, aliases, and prompt expansion. Programming +features include additional variable expansions, shell +arithmetic, and a number of variables and options to control +shell behavior. + +Bash was originally written by Brian Fox of the Free Software +Foundation. The current developer and maintainer is Chet Ramey +of Case Western Reserve University. + +A2) What's the latest version? + +The latest version is 4.1, first made available on 31 December, 2009. + +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 4.1: + +ftp://ftp.gnu.org/pub/gnu/bash/bash-4.1.tar.gz +ftp://ftp.cwru.edu/pub/bash/bash-4.1.tar.gz + +Formatted versions of the documentation are available with the URLs: + +ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-4.1.tar.gz +ftp://ftp.cwru.edu/pub/bash/bash-doc-4.1.tar.gz + +Any patches for the current version are available with the URL: + +ftp://ftp.cwru.edu/pub/bash/bash-4.1-patches/ + +A4) On what machines will bash run? + +Bash has been ported to nearly every version of Unix. All you +should have to do to build it on a machine for which a port +exists is to type `configure' and then `make'. The build process +will attempt to discover the version of Unix you have and tailor +itself accordingly, using a script created by GNU autoconf. + +More information appears in the file `INSTALL' in the distribution. + +The Bash web page (http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html) +explains how to obtain binary versions of bash for most of the major +commercial Unix systems. + +A5) Will bash run on operating systems other than Unix? + +Configuration specifics for Unix-like systems such as QNX and +LynxOS are included in the distribution. Bash-2.05 and later +versions should compile and run on Minix 2.0 (patches were +contributed), but I don't believe anyone has built bash-2.x on +earlier Minix versions yet. + +Bash has been ported to versions of Windows implementing the Win32 +programming interface. This includes Windows 95 and Windows NT. +The port was done by Cygnus Solutions (now part of Red Hat) as part +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 +ports of bash-3.2 and bash-4.0 to the CYGWIN environment, and both +are available as part of their current release. + +Bash-2.05b and later versions should require no local Cygnus changes to +build and run under CYGWIN. + +DJ Delorie has a port of bash-2.x which runs under MS-DOS, as part +of the DJGPP project. For more information on the project, see + +http://www.delorie.com/djgpp/ + +I have been told that the original DJGPP port was done by Daisuke Aoyama. + +Mark Elbrecht <snowball3@bigfoot.com> has sent me notice that bash-2.04 +is available for DJGPP V2. The files are available as: + +ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204b.zip binary +ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204d.zip documentation +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. I do not anticipate any problems +with building bash-4.1, but will gladly accept any patches that are needed. + +A6) How can I build bash with gcc? + +Bash configures to use gcc by default if it is available. Read the +file INSTALL in the distribution for more information. + +A7) How can I make bash my login shell? + +Some machines let you use `chsh' to change your login shell. Other +systems use `passwd -s' or `passwd -e'. If one of these works for +you, that's all you need. Note that many systems require the full +pathname to a shell to appear in /etc/shells before you can make it +your login shell. For this, you may need the assistance of your +friendly local system administrator. + +If you cannot do this, you can still use bash as your login shell, but +you need to perform some tricks. The basic idea is to add a command +to your login shell's startup file to replace your login shell with +bash. + +For example, if your login shell is csh or tcsh, and you have installed +bash in /usr/gnu/bin/bash, add the following line to ~/.login: + + if ( -f /usr/gnu/bin/bash ) exec /usr/gnu/bin/bash --login + +(the `--login' tells bash that it is a login shell). + +It's not a good idea to put this command into ~/.cshrc, because every +csh you run without the `-f' option, even ones started to run csh scripts, +reads that file. If you must put the command in ~/.cshrc, use something +like + + if ( $?prompt ) exec /usr/gnu/bin/bash --login + +to ensure that bash is exec'd only when the csh is interactive. + +If your login shell is sh or ksh, you have to do two things. + +First, create an empty file in your home directory named `.bash_profile'. +The existence of this file will prevent the exec'd bash from trying to +read ~/.profile, and re-execing itself over and over again. ~/.bash_profile +is the first file bash tries to read initialization commands from when +it is invoked as a login shell. + +Next, add a line similar to the above to ~/.profile: + + [ -f /usr/gnu/bin/bash ] && [ -x /usr/gnu/bin/bash ] && \ + exec /usr/gnu/bin/bash --login + +This will cause login shells to replace themselves with bash running as +a login shell. Once you have this working, you can copy your initialization +code from ~/.profile to ~/.bash_profile. + +I have received word that the recipe supplied above is insufficient for +machines running CDE. CDE has a maze of twisty little startup files, all +slightly different. + +If you cannot change your login shell in the password file to bash, you +will have to (apparently) live with CDE using the shell in the password +file to run its startup scripts. If you have changed your shell to bash, +there is code in the CDE startup files (on Solaris, at least) that attempts +to do the right thing. It is, however, often broken, and may require that +you use the $BASH_ENV trick described below. + +`dtterm' claims to use $SHELL as the default program to start, so if you +can change $SHELL in the CDE startup files, you should be able to use bash +in your terminal windows. + +Setting DTSOURCEPROFILE in ~/.dtprofile will cause the `Xsession' program +to read your login shell's startup files. You may be able to use bash for +the rest of the CDE programs by setting SHELL to bash in ~/.dtprofile as +well, but I have not tried this. + +You can use the above `exec' recipe to start bash when not logging in with +CDE by testing the value of the DT variable: + + if [ -n "$DT" ]; then + [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login + fi + +If CDE starts its shells non-interactively during login, the login shell +startup files (~/.profile, ~/.bash_profile) will not be sourced at login. +To get around this problem, append a line similar to the following to your +~/.dtprofile: + + BASH_ENV=${HOME}/.bash_profile ; export BASH_ENV + +and add the following line to the beginning of ~/.bash_profile: + + unset BASH_ENV + +A8) I just changed my login shell to bash, and now I can't FTP into my + machine. Why not? + +You must add the full pathname to bash to the file /etc/shells. As +noted in the answer to the previous question, many systems require +this before you can make bash your login shell. + +Most versions of ftpd use this file to prohibit `special' users +such as `uucp' and `news' from using FTP. + +A9) What's the `POSIX Shell and Utilities standard'? + +POSIX is a name originally coined by Richard Stallman for a +family of open system standards based on UNIX. There are a +number of aspects of UNIX under consideration for +standardization, from the basic system services at the system +call and C library level to applications and tools to system +administration and management. Each area of standardization is +assigned to a working group in the 1003 series. + +The POSIX Shell and Utilities standard was originally developed by +IEEE Working Group 1003.2 (POSIX.2). Today it has been merged with +the original 1003.1 Working Group and is maintained by the Austin +Group (a joint working group of the IEEE, The Open Group and +ISO/IEC SC22/WG15). Today the Shell and Utilities are a volume +within the set of documents that make up IEEE Std 1003.1-2001, and +thus now the former POSIX.2 (from 1992) is now part of the current +POSIX.1 standard (POSIX 1003.1-2001). + +The Shell and Utilities volume concentrates on the command +interpreter interface and utility programs commonly executed from +the command line or by other programs. The standard is freely +available on the web at http://www.UNIX-systems.org/version3/ . +Work continues at the Austin Group on maintenance issues; see +http://www.opengroup.org/austin/ to join the discussions. + +Bash is concerned with the aspects of the shell's behavior defined +by the POSIX Shell and Utilities volume. The shell command +language has of course been standardized, including the basic flow +control and program execution constructs, I/O redirection and +pipelining, argument handling, variable expansion, and quoting. + +The `special' builtins, which must be implemented as part of the +shell to provide the desired functionality, are specified as +being part of the shell; examples of these are `eval' and +`export'. Other utilities appear in the sections of POSIX not +devoted to the shell which are commonly (and in some cases must +be) implemented as builtin commands, such as `read' and `test'. +POSIX also specifies aspects of the shell's interactive +behavior as part of the UPE, including job control and command +line editing. Only vi-style line editing commands have been +standardized; emacs editing commands were left out due to +objections. + +The latest version of the POSIX Shell and Utilities standard is +available (now updated to the 2004 Edition) as part of the Single +UNIX Specification Version 3 at + +http://www.UNIX-systems.org/version3/ + +A10) What is the bash `posix mode'? + +Although bash is an implementation of the POSIX shell +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 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 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 4.1? + +Bash-4.1 is the first revision to the fourth major release of bash. + +Bash-4.1 contains the following new features (see the manual page for +complete descriptions and the CHANGES and NEWS files in the bash-4.1 +distribution): + +o Here-documents within $(...) command substitutions may once more be + delimited by the closing right paren, instead of requiring a newline. + +o Bash's file status checks (executable, readable, etc.) now take file + system ACLs into account on file systems that support them. + +o Bash now passes environment variables with names that are not valid + shell variable names through into the environment passed to child + processes. + +o The `execute-unix-command' readline function now attempts to clear and + reuse the current line rather than move to a new one after the command + executes. + +o `printf -v' can now assign values to array indices. + +o New `complete -E' and `compopt -E' options that work on the "empty" + completion: completion attempted on an empty command line. + +o New complete/compgen/compopt -D option to define a `default' completion: + a completion to be invoked on command for which no completion has been + defined. If this function returns 124, programmable completion is + attempted again, allowing a user to dynamically build a set of completions + as completion is attempted by having the default completion function + install individual completion functions each time it is invoked. + +o When displaying associative arrays, subscripts are now quoted. + +o Changes to dabbrev-expand to make it more `emacs-like': no space appended + after matches, completions are not sorted, and most recent history entries + are presented first. + +o The [[ and (( commands are now subject to the setting of `set -e' and the + ERR trap. + +o The source/. builtin now removes NUL bytes from the file before attempting + to parse commands. + +o There is a new configuration option (in config-top.h) that forces bash to + forward all history entries to syslog. + +o A new variable $BASHOPTS to export shell options settable using `shopt' to + child processes. + +o There is a new confgure option that forces the extglob option to be + enabled by default. + +o New variable $BASH_XTRACEFD; when set to an integer bash will write xtrace + output to that file descriptor. + +o If the optional left-hand-side of a redirection is of the form {var}, the + shell assigns the file descriptor used to $var or uses $var as the file + descriptor to move or close, depending on the redirection operator. + +o The < and > operators to the [[ conditional command now do string + comparison according to the current locale. + +o Programmable completion now uses the completion for `b' instead of `a' + when completion is attempted on a line like: a $(b c. + +o Force extglob on temporarily when parsing the pattern argument to + the == and != operators to the [[ command, for compatibility. + +o Changed the behavior of interrupting the wait builtin when a SIGCHLD is + received and a trap on SIGCHLD is set to be Posix-mode only. + +o The read builtin has a new `-N nchars' option, which reads exactly NCHARS + characters, ignoring delimiters like newline. + +o The mapfile/readarray builtin no longer stores the commands it invokes via + callbacks in the history list. + +o There is a new `compat40' shopt option. + +o The < and > operators to [[ do string comparisons using the current locale + only if the compatibility level is greater than 40 (set to 41 by default). + +o New bindable readline function: menu-complete-backward. + +o In the readline vi-mode insertion keymap, C-n is now bound to menu-complete + by default, and C-p to menu-complete-backward. + +o When in readline vi command mode, repeatedly hitting ESC now does nothing, + even when ESC introduces a bound key sequence. This is closer to how + historical vi behaves. + +o New bindable readline function: skip-csi-sequence. Can be used as a + default to consume key sequences generated by keys like Home and End + without having to bind all keys. + +o New bindable readline variable: skip-completed-text, active when + completing in the middle of a word. If enabled, it means that characters + in the completion that match characters in the remainder of the word are + "skipped" rather than inserted into the line. + +o The pre-readline-6.0 version of menu completion is available as + "old-menu-complete" for users who do not like the readline-6.0 version. + +o New bindable readline variable: echo-control-characters. If enabled, and + the tty ECHOCTL bit is set, controls the echoing of characters + corresponding to keyboard-generated signals. + +o New bindable readline variable: enable-meta-key. Controls whether or not + readline sends the smm/rmm sequences if the terminal indicates it has a + meta key that enables eight-bit characters. + +A short feature history dating from Bash-2.0: + +Bash-4.0 contained the following new features: + +o When using substring expansion on the positional parameters, a starting + index of 0 now causes $0 to be prefixed to the list. + +o There is a new variable, $BASHPID, which always returns the process id of + the current shell. + +o There is a new `autocd' option that, when enabled, causes bash to attempt + to `cd' to a directory name that is supplied as the first word of a + simple command. + +o There is a new `checkjobs' option that causes the shell to check for and + report any running or stopped jobs at exit. + +o The programmable completion code exports a new COMP_TYPE variable, set to + a character describing the type of completion being attempted. + +o The programmable completion code exports a new COMP_KEY variable, set to + the character that caused the completion to be invoked (e.g., TAB). + +o The programmable completion code now uses the same set of characters as + readline when breaking the command line into a list of words. + +o The block multiplier for the ulimit -c and -f options is now 512 when in + Posix mode, as Posix specifies. + +o Changed the behavior of the read builtin to save any partial input received + in the specified variable when the read builtin times out. This also + results in variables specified as arguments to read to be set to the empty + string when there is no input available. When the read builtin times out, + it returns an exit status greater than 128. + +o The shell now has the notion of a `compatibility level', controlled by + new variables settable by `shopt'. Setting this variable currently + restores the bash-3.1 behavior when processing quoted strings on the rhs + of the `=~' operator to the `[[' command. + +o The `ulimit' builtin now has new -b (socket buffer size) and -T (number + of threads) options. + +o There is a new `compopt' builtin that allows completion functions to modify + completion options for existing completions or the completion currently + being executed. + +o The `read' builtin has a new -i option which inserts text into the reply + buffer when using readline. + +o A new `-E' option to the complete builtin allows control of the default + behavior for completion on an empty line. + +o There is now limited support for completing command name words containing + globbing characters. + +o The `help' builtin now has a new -d option, to display a short description, + and a -m option, to print help information in a man page-like format. + +o There is a new `mapfile' builtin to populate an array with lines from a + given file. + +o If a command is not found, the shell attempts to execute a shell function + named `command_not_found_handle', supplying the command words as the + function arguments. + +o There is a new shell option: `globstar'. When enabled, the globbing code + treats `**' specially -- it matches all directories (and files within + them, when appropriate) recursively. + +o There is a new shell option: `dirspell'. When enabled, the filename + completion code performs spelling correction on directory names during + completion. + +o The `-t' option to the `read' builtin now supports fractional timeout + values. + +o Brace expansion now allows zero-padding of expanded numeric values and + will add the proper number of zeroes to make sure all values contain the + same number of digits. + +o There is a new bash-specific bindable readline function: `dabbrev-expand'. + It uses menu completion on a set of words taken from the history list. + +o The command assigned to a key sequence with `bind -x' now sets two new + variables in the environment of the executed command: READLINE_LINE_BUFFER + and READLINE_POINT. The command can change the current readline line + and cursor position by modifying READLINE_LINE_BUFFER and READLINE_POINT, + respectively. + +o There is a new >>& redirection operator, which appends the standard output + and standard error to the named file. + +o The parser now understands `|&' as a synonym for `2>&1 |', which redirects + the standard error for a command through a pipe. + +o The new `;&' case statement action list terminator causes execution to + continue with the action associated with the next pattern in the + statement rather than terminating the command. + +o The new `;;&' case statement action list terminator causes the shell to + test the next set of patterns after completing execution of the current + action, rather than terminating the command. + +o The shell understands a new variable: PROMPT_DIRTRIM. When set to an + integer value greater than zero, prompt expansion of \w and \W will + retain only that number of trailing pathname components and replace + the intervening characters with `...'. + +o There are new case-modifying word expansions: uppercase (^[^]) and + lowercase (,[,]). They can work on either the first character or + array element, or globally. They accept an optional shell pattern + that determines which characters to modify. There is an optionally- + configured feature to include capitalization operators. + +o The shell provides associative array variables, with the appropriate + support to create, delete, assign values to, and expand them. + +o The `declare' builtin now has new -l (convert value to lowercase upon + assignment) and -u (convert value to uppercase upon assignment) options. + There is an optionally-configurable -c option to capitalize a value at + assignment. + +o There is a new `coproc' reserved word that specifies a coprocess: an + asynchronous command run with two pipes connected to the creating shell. + Coprocs can be named. The input and output file descriptors and the + PID of the coprocess are available to the calling shell in variables + with coproc-specific names. + +o A value of 0 for the -t option to `read' now returns success if there is + input available to be read from the specified file descriptor. + +o CDPATH and GLOBIGNORE are ignored when the shell is running in privileged + mode. + +o New bindable readline functions shell-forward-word and shell-backward-word, + which move forward and backward words delimited by shell metacharacters + and honor shell quoting. + +o New bindable readline functions shell-backward-kill-word and shell-kill-word + which kill words backward and forward, but use the same word boundaries + as shell-forward-word and shell-backward-word. + +Bash-3.2 contained the following new features: + +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. + +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 + +o HISTCONTROL is now a colon-separated list of options and has been + extended with a new `erasedups' option that will result in only one + copy of a command being kept in the history list + +o Brace expansion has been extended with a new {x..y} form, producing + sequences of digits or characters + +o Timestamps are now kept with history entries, with an option to save + and restore them from the history file; there is a new HISTTIMEFORMAT + variable describing how to display the timestamps when listing history + entries + +o The `[[' command can now perform extended regular expression (egrep-like) + matching, with matched subexpressions placed in the BASH_REMATCH array + variable + +o A new `pipefail' option causes a pipeline to return a failure status if + any command in it fails + +o The `jobs', `kill', and `wait' builtins now accept job control notation + in their arguments even if job control is not enabled + +o The `gettext' package and libintl have been integrated, and the shell + messages may be translated into other languages + +Bash-2.05b introduced the following new features: + +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 + +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 + login shells and unset otherwise + +o New `\A' prompt string escape sequence; expanding to time in 24-hour + HH:MM format + +o New `-A group/-g' option to complete and compgen; goes group name + completion + +o New [+-]O invocation option to set and unset `shopt' options at startup + +o ksh-like `ERR' trap + +o `for' loops now allow empty word lists after the `in' reserved word + +o new `hard' and `soft' arguments for the `ulimit' builtin + +o Readline can be configured to place the user at the same point on the line + when retrieving commands from the history list + +o Readline can be configured to skip `hidden' files (filenames with a leading + `.' on Unix) when performing completion + +Bash-2.05 introduced the following new features: + +o This version has once again reverted to using locales and strcoll(3) when + processing pattern matching bracket expressions, as POSIX requires. +o Added a new `--init-file' invocation argument as a synonym for `--rcfile', + per the new GNU coding standards. +o The /dev/tcp and /dev/udp redirections now accept service names as well as + port numbers. +o `complete' and `compgen' now take a `-o value' option, which controls some + of the aspects of that compspec. Valid values are: + + default - perform bash default completion if programmable + completion produces no matches + dirnames - perform directory name completion if programmable + completion produces no matches + filenames - tell readline that the compspec produces filenames, + so it can do things like append slashes to + directory names and suppress trailing spaces +o A new loadable builtin, realpath, which canonicalizes and expands symlinks + in pathname arguments. +o When `set' is called without options, it prints function defintions in a + way that allows them to be reused as input. This affects `declare' and + `declare -p' as well. This only happens when the shell is not in POSIX + mode, since POSIX.2 forbids this behavior. + +Bash-2.04 introduced the following new features: + +o Programmable word completion with the new `complete' and `compgen' builtins; + examples are provided in examples/complete/complete-examples +o `history' has a new `-d' option to delete a history entry +o `bind' has a new `-x' option to bind key sequences to shell commands +o The prompt expansion code has new `\j' and `\l' escape sequences +o The `no_empty_cmd_completion' shell option, if enabled, inhibits + command completion when TAB is typed on an empty line +o `help' has a new `-s' option to print a usage synopsis +o New arithmetic operators: var++, var--, ++var, --var, expr1,expr2 (comma) +o New ksh93-style arithmetic for command: + for ((expr1 ; expr2; expr3 )); do list; done +o `read' has new options: `-t', `-n', `-d', `-s' +o The redirection code handles several filenames specially: /dev/fd/N, + /dev/stdin, /dev/stdout, /dev/stderr +o The redirection code now recognizes /dev/tcp/HOST/PORT and + /dev/udp/HOST/PORT and tries to open a TCP or UDP socket, respectively, + to the specified port on the specified host +o The ${!prefix*} expansion has been implemented +o A new FUNCNAME variable, which expands to the name of a currently-executing + function +o The GROUPS variable is no longer readonly +o A new shopt `xpg_echo' variable, to control the behavior of echo with + respect to backslash-escape sequences at runtime +o The NON_INTERACTIVE_LOGIN_SHELLS #define has returned + +The version of Readline released with Bash-2.04, Readline-4.1, had several +new features as well: + +o Parentheses matching is always compiled into readline, and controllable + with the new `blink-matching-paren' variable +o The history-search-forward and history-search-backward functions now leave + point at the end of the line when the search string is empty, like + reverse-search-history, and forward-search-history +o A new function for applications: rl_on_new_line_with_prompt() +o New variables for applications: rl_already_prompted, and rl_gnu_readline_p + + +Bash-2.03 had very few new features, in keeping with the convention +that odd-numbered releases provide mainly bug fixes. A number of new +features were added to Readline, mostly at the request of the Cygnus +folks. + +A new shopt option, `restricted_shell', so that startup files can test + whether or not the shell was started in restricted mode +Filename generation is now performed on the words between ( and ) in + compound array assignments (this is really a bug fix) +OLDPWD is now auto-exported, as POSIX.2 requires +ENV and BASH_ENV are read-only variables in a restricted shell +Bash may now be linked against an already-installed Readline library, + as long as the Readline library is version 4 or newer +All shells begun with the `--login' option will source the login shell + startup files, even if the shell is not interactive + +There were lots of changes to the version of the Readline library released +along with Bash-2.03. For a complete list of the changes, read the file +CHANGES in the Bash-2.03 distribution. + +Bash-2.02 contained the following new features: + +a new version of malloc (based on the old GNU malloc code in previous + bash versions) that is more page-oriented, more conservative + with memory usage, does not `orphan' large blocks when they + are freed, is usable on 64-bit machines, and has allocation + checking turned on unconditionally +POSIX.2-style globbing character classes ([:alpha:], [:alnum:], etc.) +POSIX.2-style globbing equivalence classes +POSIX.2-style globbing collating symbols +the ksh [[...]] extended conditional command +the ksh egrep-style extended pattern matching operators +a new `printf' builtin +the ksh-like $(<filename) command substitution, which is equivalent to + $(cat filename) +new tilde prefixes that expand to directories from the directory stack +new `**' arithmetic operator to do exponentiation +case-insensitive globbing (filename expansion) +menu completion a la tcsh +`magic-space' history expansion function like tcsh +the readline inputrc `language' has a new file inclusion directive ($include) + +Bash-2.01 contained only a few new features: + +new `GROUPS' builtin array variable containing the user's group list +new bindable readline commands: history-and-alias-expand-line and + alias-expand-line + +Bash-2.0 contained extensive changes and new features from bash-1.14.7. +Here's a short list: + +new `time' reserved word to time pipelines, shell builtins, and + shell functions +one-dimensional arrays with a new compound assignment statement, + appropriate expansion constructs and modifications to some + of the builtins (read, declare, etc.) to use them +new quoting syntaxes for ANSI-C string expansion and locale-specific + string translation +new expansions to do substring extraction, pattern replacement, and + indirect variable expansion +new builtins: `disown' and `shopt' +new variables: HISTIGNORE, SHELLOPTS, PIPESTATUS, DIRSTACK, GLOBIGNORE, + MACHTYPE, BASH_VERSINFO +special handling of many unused or redundant variables removed + (e.g., $notify, $glob_dot_filenames, $no_exit_on_failed_exec) +dynamic loading of new builtin commands; many loadable examples provided +new prompt expansions: \a, \e, \n, \H, \T, \@, \v, \V +history and aliases available in shell scripts +new readline variables: enable-keypad, mark-directories, input-meta, + visible-stats, disable-completion, comment-begin +new readline commands to manipulate the mark and operate on the region +new readline emacs mode commands and bindings for ksh-88 compatibility +updated and extended builtins +new DEBUG trap +expanded (and now documented) restricted shell mode + +implementation stuff: +autoconf-based configuration +nearly all of the bugs reported since version 1.14 have been fixed +most builtins converted to use builtin `getopt' for consistency +most builtins use -p option to display output in a reusable form + (for consistency) +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-4.1 and + previous bash versions? + +There are a few incompatibilities between version 4.1 and previous +versions. 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 (or bug-bash@gnu.org if you would like +community discussion) if if you find something that's not mentioned there. + +Section C: Differences from other Unix shells + +C1) How does bash differ from sh, the Bourne shell? + +This is a non-comprehensive list of features that differentiate bash +from the SVR4.2 shell. The bash manual page explains these more +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 + the `select' compound command and reserved word + arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done + new $'...' and $"..." quoting + the $(...) form of command substitution + the $(<filename) form of command substitution, equivalent to + $(cat filename) + the ${#param} parameter value length operator + the ${!param} indirect parameter expansion operator + the ${!param*} prefix expansion 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} + variables: BASH, BASHPID, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY, + TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS, + LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME, + ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE, + HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS, + PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC, + SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars, + auto_resume, PROMPT_DIRTRIM, BASHOPTS, BASH_XTRACEFD + DEBUG trap + ERR trap + variable arrays with new compound assignment syntax + 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 -d/-l/-p/-t. + export -n/-f/-p/name=value, pwd -L/-P, + read -e/-p/-a/-t/-n/-d/-s/-u/-i/-N, + readonly -a/-f/name=value, trap -l, set +o, + set -b/-m/-o option/-h/-p/-B/-C/-H/-P, + 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 + bash restricted shell mode is more extensive + bash allows functions and variables with the same name + brace expansion + tilde expansion + arithmetic expansion with $((...)) and `let' builtin + the `[[...]]' extended conditional command + process substitution + aliases and alias/unalias builtins + local variables in functions and `local' builtin + readline and command-line editing with programmable completion + command history and history/fc builtins + csh-like history expansion + other new bash builtins: bind, command, compgen, complete, builtin, + declare/typeset, dirs, enable, fc, help, + history, logout, popd, pushd, disown, shopt, + printf, compopt, mapfile + exported functions + filename generation when using output redirection (command >a*) + POSIX.2-style globbing character classes + POSIX.2-style globbing equivalence classes + POSIX.2-style globbing collating symbols + egrep-like extended pattern matching operators + case-insensitive pattern matching and globbing + variable assignments preceding commands affect only that command, + even for builtins and functions + 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 + autocd shell option and behavior + command-not-found hook with command_not_found_handle shell function + globstar shell option and `**' globbing behavior + |& synonym for `2>&1 |' + ;& and ;;& case action list terminators + case-modifying word expansions and variable attributes + associative arrays + coprocesses using the `coproc' reserved word and variables + shell assignment of a file descriptor used in a redirection to a variable + +Things sh has that bash does not: + uses variable SHACCT to do shell accounting + includes `stop' builtin (bash can use alias stop='kill -s STOP') + `newgrp' builtin + turns on job control if called as `jsh' + $TIMEOUT (like bash $TMOUT) + `^' is a synonym for `|' + new SVR4.2 sh builtins: mldmode, priv + +Implementation differences: + redirection to/from compound commands causes sh to create a subshell + bash does not allow unbalanced quotes; sh silently inserts them at EOF + bash does not mess with signal 11 + sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100 + bash splits only the results of expansions on IFS, using POSIX.2 + field splitting rules; sh splits all words on IFS + sh does not allow MAILCHECK to be unset (?) + sh does not allow traps on SIGALRM or SIGCHLD + bash allows multiple option arguments when invoked (e.g. -x -v); + sh allows only a single option argument (`sh -x -v' attempts + to open a file named `-v', and, on SunOS 4.1.4, dumps core. + On Solaris 2.4 and earlier versions, sh goes into an infinite + loop.) + sh exits a script if any builtin fails; bash exits only if one of + the POSIX.2 `special' builtins fails + +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:offset[:length]} parameter substring operator + the ${param/pat[/string]} parameter pattern substitution operator + variables: BASH, BASH_VERSION, BASH_VERSINFO, BASHPID, UID, EUID, SHLVL, + TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, + HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND, + IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK, + PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE, + GROUPS, FUNCNAME, histchars, auto_resume, PROMPT_DIRTRIM + prompt expansion with backslash escapes and command substitution + 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, + jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd, + read -e/-p/-a/-t/-n/-d/-s/-N, readonly -a/-n/-f/-p, + 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 -i/-q/-u/-x, umask -S, alias -p, + shopt, disown, printf, complete, compgen, compopt, mapfile + `!' csh-style history expansion + POSIX.2-style globbing character classes + POSIX.2-style globbing equivalence classes + POSIX.2-style globbing collating symbols + egrep-like extended pattern matching operators + case-insensitive pattern matching and globbing + `**' 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' + debugger support, including the `caller' builtin + RETURN trap + Timestamps in history entries + {x..y} brace expansion + The `+=' assignment operator + autocd shell option and behavior + command-not-found hook with command_not_found_handle shell function + globstar shell option and `**' globbing behavior + |& synonym for `2>&1 |' + ;& and ;;& case action list terminators + case-modifying word expansions and variable attributes + associative arrays + coprocesses using the `coproc' reserved word and variables + shell assignment of a file descriptor used in a redirection to a variable + +Things ksh88 has or uses that bash does not: + tracked aliases (alias -t) + variables: ERRNO, FPATH, EDITOR, VISUAL + co-processes (bash uses different syntax) + weirdly-scoped functions + 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, newgrp, print, + read -p/-s/var?prompt, set -A/-o gmacs/ + -o bgnice/-o markdirs/-o trackall/-o viraw/-s, + typeset -H/-L/-R/-Z/-A/-ft/-fu/-fx/-t, whence + using environment to pass attributes of exported variables + arithmetic evaluation done on arguments to some builtins + reads .profile from $PWD when invoked as login shell + +Implementation differences: + ksh runs last command of a pipeline in parent shell context + bash has brace expansion by default (ksh88 compile-time option) + bash has fixed startup file for all interactive shells; ksh reads $ENV + bash has exported functions + bash command search finds functions before builtins + bash waits for all commands in pipeline to exit before returning status + emacs-mode editing has some slightly different key bindings + +C3) Which new features in ksh-93 are not in bash, and which are? + +This list is current through ksh93t+ (05/05/2009) + +New things in ksh-93 not in bash-4.1: + floating point arithmetic and variables + math library functions + ${!name[sub]} name of subscript for associative array + `.' is allowed in variable names to create a hierarchical namespace + more extensive compound assignment syntax + discipline functions + KEYBD trap + variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, .sh.version, + .sh.name, .sh.subscript, .sh.value, .sh.match, HISTEDIT + backreferences in pattern matching (\N) + `&' operator in pattern lists for matching (match all instead of any) + exit statuses between 0 and 255 + FPATH and PATH mixing + lexical scoping for local variables in `ksh' functions + no scoping for local variables in `POSIX' functions + $'' \C[.collating-element.] escape sequence + -C/-I invocation options + print -f (bash uses printf) + `fc' has been renamed to `hist' + `.' can execute shell functions + getopts -a + printf %B, %H, %P, %R, %T, %Z modifiers, output base for %d, `=' flag + read -n/-N differ/-v + set -o showme/-o multiline (bash default) + `sleep' and `getconf' builtins (bash has loadable versions) + typeset -n and `nameref' variables + [[ -R name ]] (checks whether or not name is a nameref) + typeset -C/-S/-T/-X/-h/-s + experimental `type' definitions (a la typedef) using typeset + negative subscripts for indexed array variables + array expansions ${array[sub1..sub2]} and ${!array[sub1..sub2]} + associative array assignments using `;' as element separator + command substitution $(n<#) expands to current byte offset for fd N + new '${ ' form of command substitution, executed in current shell + new >;/<>;/<#pat/<##pat/<#/># redirections + brace expansion printf-like formats + [[ -v var ]] operators (checks whether or not var is set) + +New things in ksh-93 present in bash-4.1: + associative arrays + [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]}, + ${!param*} + compound array assignment + the `!' reserved word + loadable builtins -- but ksh uses `builtin' while bash uses `enable' + new $'...' and $"..." quoting + FIGNORE (but bash uses GLOBIGNORE), HISTCMD + brace expansion and set -B + changes to kill builtin + `command', `builtin', `disown' builtins + echo -e + exec -c/-a + read -A (bash uses read -a) + read -t/-d + trap -p + `.' restores the positional parameters when it completes + set -o notify/-C + set -o pipefail + set -G (-o globstar) and ** + POSIX.2 `test' + umask -S + unalias -a + command and arithmetic substitution performed on PS1, PS4, and ENV + command name completion, TAB displaying possible completions + ENV processed only for interactive shells + The `+=' assignment operator + the `;&' case statement "fallthrough" pattern list terminator + csh-style history expansion and set -H + negative offsets in ${param:offset:length} + redirection operators preceded with {varname} to store fd number in varname + DEBUG can force skipping following command + +Section D: Why does bash do some things differently than other Unix shells? + +D1) Why does bash run a different version of `command' than + `which command' says it will? + +On many systems, `which' is actually a csh script that assumes +you're running csh. In tcsh, `which' and its cousin `where' +are builtins. On other Unix systems, `which' is a perl script +that uses the PATH environment variable. Many Linux distributions +use GNU `which', which is a C program that can understand shell +aliases. + +The csh script version reads the csh startup files from your +home directory and uses those to determine which `command' will +be invoked. Since bash doesn't use any of those startup files, +there's a good chance that your bash environment differs from +your csh environment. The bash `type' builtin does everything +`which' does, and will report correct results for the running +shell. If you're really wedded to the name `which', try adding +the following function definition to your .bashrc: + + which() + { + builtin type "$@" + } + +If you're moving from tcsh and would like to bring `where' along +as well, use this function: + + where() + { + builtin type -a "$@" + } + +D2) Why doesn't bash treat brace expansions exactly like csh? + +The only difference between bash and csh brace expansion is that +bash requires a brace expression to contain at least one unquoted +comma if it is to be expanded. Any brace-surrounded word not +containing an unquoted comma is left unchanged by the brace +expansion code. This affords the greatest degree of sh +compatibility. + +Bash, ksh, zsh, and pd-ksh all implement brace expansion this way. + +D3) Why doesn't bash have csh variable modifiers? + +Posix has specified a more powerful, albeit somewhat more cryptic, +mechanism cribbed from ksh, and bash implements it. + +${parameter%word} + Remove smallest suffix pattern. The WORD is expanded to produce + a pattern. It then expands to the value of PARAMETER, with the + smallest portion of the suffix matched by the pattern deleted. + + x=file.c + echo ${x%.c}.o + -->file.o + +${parameter%%word} + + Remove largest suffix pattern. The WORD is expanded to produce + a pattern. It then expands to the value of PARAMETER, with the + largest portion of the suffix matched by the pattern deleted. + + x=posix/src/std + echo ${x%%/*} + -->posix + +${parameter#word} + Remove smallest prefix pattern. The WORD is expanded to produce + a pattern. It then expands to the value of PARAMETER, with the + smallest portion of the prefix matched by the pattern deleted. + + x=$HOME/src/cmd + echo ${x#$HOME} + -->/src/cmd + +${parameter##word} + Remove largest prefix pattern. The WORD is expanded to produce + a pattern. It then expands to the value of PARAMETER, with the + largest portion of the prefix matched by the pattern deleted. + + x=/one/two/three + echo ${x##*/} + -->three + + +Given + a=/a/b/c/d + b=b.xxx + + csh bash result + --- ---- ------ + $a:h ${a%/*} /a/b/c + $a:t ${a##*/} d + $b:r ${b%.*} b + $b:e ${b##*.} xxx + + +D4) How can I make my csh aliases work when I convert to bash? + +Bash uses a different syntax to support aliases than csh does. +The details can be found in the documentation. We have provided +a shell script which does most of the work of conversion for you; +this script can be found in ./examples/misc/aliasconv.sh. Here is +how you use it: + +Start csh in the normal way for you. (e.g., `csh') + +Pipe the output of `alias' through `aliasconv.sh', saving the +results into `bash_aliases': + + alias | bash aliasconv.sh >bash_aliases + +Edit `bash_aliases', carefully reading through any created +functions. You will need to change the names of some csh specific +variables to the bash equivalents. The script converts $cwd to +$PWD, $term to $TERM, $home to $HOME, $user to $USER, and $prompt +to $PS1. You may also have to add quotes to avoid unwanted +expansion. + +For example, the csh alias: + + alias cd 'cd \!*; echo $cwd' + +is converted to the bash function: + + cd () { command cd "$@"; echo $PWD ; } + +The only thing that needs to be done is to quote $PWD: + + cd () { command cd "$@"; echo "$PWD" ; } + +Merge the edited file into your ~/.bashrc. + +There is an additional, more ambitious, script in +examples/misc/cshtobash that attempts to convert your entire csh +environment to its bash equivalent. This script can be run as +simply `cshtobash' to convert your normal interactive +environment, or as `cshtobash ~/.login' to convert your login +environment. + +D5) How can I pipe standard output and standard error from one command to + another, like csh does with `|&'? + +Use + command 2>&1 | command2 + +The key is to remember that piping is performed before redirection, so +file descriptor 1 points to the pipe when it is duplicated onto file +descriptor 2. + +D6) Now that I've converted from ksh to bash, are there equivalents to + ksh features like autoloaded functions and the `whence' command? + +There are features in ksh-88 and ksh-93 that do not have direct bash +equivalents. Most, however, can be emulated with very little trouble. + +ksh-88 feature Bash equivalent +-------------- --------------- +compiled-in aliases set up aliases in .bashrc; some ksh aliases are + bash builtins (hash, history, type) +coprocesses named pipe pairs (one for read, one for write) +typeset +f declare -F +cd, print, whence function substitutes in examples/functions/kshenv +autoloaded functions examples/functions/autoload is the same as typeset -fu +read var?prompt read -p prompt var + +ksh-93 feature Bash equivalent +-------------- --------------- +sleep, getconf Bash has loadable versions in examples/loadables +${.sh.version} $BASH_VERSION +print -f printf +hist alias hist=fc +$HISTEDIT $FCEDIT + +Section E: How can I get bash to do certain things, and why does bash do + things the way it does? + +E1) Why is the bash builtin `test' slightly different from /bin/test? + +The specific example used here is [ ! x -o x ], which is false. + +Bash's builtin `test' implements the Posix.2 spec, which can be +summarized as follows (the wording is due to David Korn): + +Here is the set of rules for processing test arguments. + + 0 Args: False + 1 Arg: True iff argument is not null. + 2 Args: If first arg is !, True iff second argument is null. + If first argument is unary, then true if unary test is true + Otherwise error. + 3 Args: If second argument is a binary operator, do binary test of $1 $3 + If first argument is !, negate two argument test of $2 $3 + If first argument is `(' and third argument is `)', do the + one-argument test of the second argument. + Otherwise error. + 4 Args: If first argument is !, negate three argument test of $2 $3 $4. + Otherwise unspecified + 5 or more Args: unspecified. (Historical shells would use their + current algorithm). + +The operators -a and -o are considered binary operators for the purpose +of the 3 Arg case. + +As you can see, the test becomes (not (x or x)), which is false. + +E2) Why does bash sometimes say `Broken pipe'? + +If a sequence of commands appears in a pipeline, and one of the +reading commands finishes before the writer has finished, the +writer receives a SIGPIPE signal. Many other shells special-case +SIGPIPE as an exit status in the pipeline and do not report it. +For example, in: + + ps -aux | head + +`head' can finish before `ps' writes all of its output, and ps +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. + +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? + +Readline, the line editing library that bash uses, does not know +that the terminal escape sequences do not take up space on the +screen. The redisplay code assumes, unless told otherwise, that +each character in the prompt is a `printable' character that +takes up one character position on the screen. + +You can use the bash prompt expansion facility (see the PROMPTING +section in the manual page) to tell readline that sequences of +characters in the prompt strings take up no screen space. + +Use the \[ escape to begin a sequence of non-printing characters, +and the \] escape to signal the end of such a sequence. + +E4) If I pipe the output of a command into `read variable', why doesn't + the output show up in $variable when the read command finishes? + +This has to do with the parent-child relationship between Unix +processes. It affects all commands run in pipelines, not just +simple calls to `read'. For example, piping a command's output +into a `while' loop that repeatedly calls `read' will result in +the same behavior. + +Each element of a pipeline, even a builtin or shell function, +runs in a separate process, a child of the shell running the +pipeline. A subprocess cannot affect its parent's environment. +When the `read' command sets the variable to the input, that +variable is set only in the subshell, not the parent shell. When +the subshell exits, the value of the variable is lost. + +Many pipelines that end with `read variable' can be converted +into command substitutions, which will capture the output of +a specified command. The output can then be assigned to a +variable: + + grep ^gnu /usr/lib/news/active | wc -l | read ngroup + +can be converted into + + ngroup=$(grep ^gnu /usr/lib/news/active | wc -l) + +This does not, unfortunately, work to split the text among +multiple variables, as read does when given multiple variable +arguments. If you need to do this, you can either use the +command substitution above to read the output into a variable +and chop up the variable using the bash pattern removal +expansion operators or use some variant of the following +approach. + +Say /usr/local/bin/ipaddr is the following shell script: + +#! /bin/sh +host `hostname` | awk '/address/ {print $NF}' + +Instead of using + + /usr/local/bin/ipaddr | read A B C D + +to break the local machine's IP address into separate octets, use + + OIFS="$IFS" + IFS=. + set -- $(/usr/local/bin/ipaddr) + IFS="$OIFS" + A="$1" B="$2" C="$3" D="$4" + +Beware, however, that this will change the shell's positional +parameters. If you need them, you should save them before doing +this. + +This is the general approach -- in most cases you will not need to +set $IFS to a different value. + +Some other user-supplied alternatives include: + +read A B C D << HERE + $(IFS=.; echo $(/usr/local/bin/ipaddr)) +HERE + +and, where process substitution is available, + +read A B C D < <(IFS=.; echo $(/usr/local/bin/ipaddr)) + +E5) I have a bunch of shell scripts that use backslash-escaped characters + in arguments to `echo'. Bash doesn't interpret these characters. Why + not, and how can I make it understand them? + +This is the behavior of echo on most Unix System V machines. + +The bash builtin `echo' is modeled after the 9th Edition +Research Unix version of `echo'. It does not interpret +backslash-escaped characters in its argument strings by default; +it requires the use of the -e option to enable the +interpretation. The System V echo provides no way to disable the +special characters; the bash echo has a -E option to disable +them. + +There is a configuration option that will make bash behave like +the System V echo and interpret things like `\t' by default. Run +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 +change the behavior of echo at runtime. Enabling this option turns +on expansion of backslash-escape sequences. + +E6) Why doesn't a while or for loop get suspended when I type ^Z? + +This is a consequence of how job control works on Unix. The only +thing that can be suspended is the process group. This is a single +command or pipeline of commands that the shell forks and executes. + +When you run a while or for loop, the only thing that the shell forks +and executes are any commands in the while loop test and commands in +the loop bodies. These, therefore, are the only things that can be +suspended when you type ^Z. + +If you want to be able to stop the entire loop, you need to put it +within parentheses, which will force the loop into a subshell that +may be stopped (and subsequently restarted) as a single unit. + +E7) What about empty for loops in Makefiles? + +It's fairly common to see constructs like this in automatically-generated +Makefiles: + +SUBDIRS = @SUBDIRS@ + + ... + +subdirs-clean: + for d in ${SUBDIRS}; do \ + ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ + done + +When SUBDIRS is empty, this results in a command like this being passed to +bash: + + for d in ; do + ( cd $d && ${MAKE} ${MFLAGS} clean ) + done + +In versions of bash before bash-2.05a, this was a syntax error. If the +reserved word `in' was present, a word must follow it before the semicolon +or newline. The language in the manual page referring to the list of words +being empty referred to the list after it is expanded. These versions of +bash required that there be at least one word following the `in' when the +construct was parsed. + +The idiomatic Makefile solution is something like: + +SUBDIRS = @SUBDIRS@ + +subdirs-clean: + subdirs=$SUBDIRS ; for d in $$subdirs; do \ + ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ + done + +The latest updated POSIX standard has changed this: the word list +is no longer required. Bash versions 2.05a and later accept the +new syntax. + +E8) Why does the arithmetic evaluation code complain about `08'? + +The bash arithmetic evaluation code (used for `let', $(()), (()), and in +other places), interprets a leading `0' in numeric constants as denoting +an octal number, and a leading `0x' as denoting hexadecimal. This is +in accordance with the POSIX.2 spec, section 2.9.2.1, which states that +arithmetic constants should be handled as signed long integers as defined +by the ANSI/ISO C standard. + +The POSIX.2 interpretation committee has confirmed this: + +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-2.03, 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 +result in the traditional behavior ([A-Z] matches all uppercase ASCII +characters). Many other locales, including the en_US locale (the default +on many US versions of Linux) collate the upper and lower case letters like +this: + + AaBb...Zz + +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. + +Look at the manual pages for setlocale(3), strcoll(3), and, if it is +present, locale(1). If you have locale(1), you can use it to find +your current locale information even if you do not have any of the +LC_ variables set. + +My advice is to put + + export LC_COLLATE=C + +into /etc/profile and inspect any shell scripts run from cron for +constructs like [A-Z]. This will prevent things like + + rm [A-Z]* + +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'. + +E11) If I resize my xterm while another program is running, why doesn't bash + notice the change? + +This is another issue that deals with job control. + +The kernel maintains a notion of a current terminal process group. Members +of this process group (processes whose process group ID is equal to the +current terminal process group ID) receive terminal-generated signals like +SIGWINCH. (For more details, see the JOB CONTROL section of the bash +man page.) + +If a terminal is resized, the kernel sends SIGWINCH to each member of +the terminal's current process group (the `foreground' process group). + +When bash is running with job control enabled, each pipeline (which may be +a single command) is run in its own process group, different from bash's +process group. This foreground process group receives the SIGWINCH; bash +does not. Bash has no way of knowing that the terminal has been resized. + +There is a `checkwinsize' option, settable with the `shopt' builtin, that +will cause bash to check the window size and adjust its idea of the +terminal's dimensions each time a process stops or exits and returns control +of the terminal to bash. Enable it with `shopt -s checkwinsize'. + +E12) Why don't negative offsets in substring expansion work like I expect? + +When substring expansion of the form ${param:offset[:length} is used, +an `offset' that evaluates to a number less than zero counts back from +the end of the expanded value of $param. + +When a negative `offset' begins with a minus sign, however, unexpected things +can happen. Consider + + a=12345678 + echo ${a:-4} + +intending to print the last four characters of $a. The problem is that +${param:-word} already has a well-defined meaning: expand to word if the +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. + +E14) Why does quoting the pattern argument to the regular expression matching + conditional operator (=~) cause regexp matching to stop working? + +In versions of bash prior to bash-3.2, the effect of quoting the regular +expression argument to the [[ command's =~ operator was not specified. +The practical effect was that double-quoting the pattern argument required +backslashes to quote special pattern characters, which interfered with the +backslash processing performed by double-quoted word expansion and was +inconsistent with how the == shell pattern matching operator treated +quoted characters. + +In bash-3.2, the shell was changed to internally quote characters in single- +and double-quoted string arguments to the =~ operator, which suppresses the +special meaning of the characters special to regular expression processing +(`.', `[', `\', `(', `), `*', `+', `?', `{', `|', `^', and `$') and forces +them to be matched literally. This is consistent with how the `==' pattern +matching operator treats quoted portions of its pattern argument. + +Since the treatment of quoted string arguments was changed, several issues +have arisen, chief among them the problem of white space in pattern arguments +and the differing treatment of quoted strings between bash-3.1 and bash-3.2. +Both problems may be solved by using a shell variable to hold the pattern. +Since word splitting is not performed when expanding shell variables in all +operands of the [[ command, this allows users to quote patterns as they wish +when assigning the variable, then expand the values to a single string that +may contain whitespace. The first problem may be solved by using backslashes +or any other quoting mechanism to escape the white space in the patterns. + +Bash-4.0 introduces the concept of a `compatibility level', controlled by +several options to the `shopt' builtin. If the `compat31' option is enabled, +bash reverts to the bash-3.1 behavior with respect to quoting the rhs of +the =~ operator. + +E15) Tell me more about the shell compatibility level. + +Bash-4.0 introduced the concept of a `shell compatibility level', specified +as a set of options to the shopt builtin (compat31, compat32, compat40 at +this writing). There is only one current compatibility level -- each +option is mutually exclusive. This list does not mention behavior that is +standard for a particular version (e.g., setting compat32 means that quoting +the rhs of the regexp matching operator quotes special regexp characters in +the word, which is default behavior in bash-3.2 and above). + +compat31 set + - the < and > operators to the [[ command do not consider the current + locale when comparing strings + - quoting the rhs of the regexp matching operator (=~) has no + special effect + +compat32 set + - the < and > operators to the [[ command do not consider the current + locale when comparing strings + +compat40 set + - the < and > operators to the [[ command do not consider the current + locale when comparing strings + - interrupting a command list such as "a ; b ; c" causes the execution + of the entire list to be aborted + +Section F: Things to watch out for on certain Unix versions + +F1) Why can't I use command line editing in my `cmdtool'? + +The problem is `cmdtool' and bash fighting over the input. When +scrolling is enabled in a cmdtool window, cmdtool puts the tty in +`raw mode' to permit command-line editing using the mouse for +applications that cannot do it themselves. As a result, bash and +cmdtool each try to read keyboard input immediately, with neither +getting enough of it to be useful. + +This mode also causes cmdtool to not implement many of the +terminal functions and control sequences appearing in the +`sun-cmd' termcap entry. For a more complete explanation, see +that file examples/suncmd.termcap in the bash distribution. + +`xterm' is a better choice, and gets along with bash much more +smoothly. + +If you must use cmdtool, you can use the termcap description in +examples/suncmd.termcap. Set the TERMCAP variable to the terminal +description contained in that file, i.e. + +TERMCAP='Mu|sun-cmd:am:bs:km:pt:li#34:co#80:cl=^L:ce=\E[K:cd=\E[J:rs=\E[s:' + +Then export TERMCAP and start a new cmdtool window from that shell. +The bash command-line editing should behave better in the new +cmdtool. If this works, you can put the assignment to TERMCAP +in your bashrc file. + +F2) I built bash on Solaris 2. Why do globbing expansions and filename + completion chop off the first few characters of each filename? + +This is the consequence of building bash on SunOS 5 and linking +with the libraries in /usr/ucblib, but using the definitions +and structures from files in /usr/include. + +The actual conflict is between the dirent structure in +/usr/include/dirent.h and the struct returned by the version of +`readdir' in libucb.a (a 4.3-BSD style `struct direct'). + +Make sure you've got /usr/ccs/bin ahead of /usr/ucb in your $PATH +when configuring and building bash. This will ensure that you +use /usr/ccs/bin/cc or acc instead of /usr/ucb/cc and that you +link with libc before libucb. + +If you have installed the Sun C compiler, you may also need to +put /usr/ccs/bin and /opt/SUNWspro/bin into your $PATH before +/usr/ucb. + +F3) Why does bash dump core after I interrupt username completion or + `~user' tilde expansion on a machine running NIS? + +This is a famous and long-standing bug in the SunOS YP (sorry, NIS) +client library, which is part of libc. + +The YP library code keeps static state -- a pointer into the data +returned from the server. When YP initializes itself (setpwent), +it looks at this pointer and calls free on it if it's non-null. +So far, so good. + +If one of the YP functions is interrupted during getpwent (the +exact function is interpretwithsave()), and returns NULL, the +pointer is freed without being reset to NULL, and the function +returns. The next time getpwent is called, it sees that this +pointer is non-null, calls free, and the bash free() blows up +because it's being asked to free freed memory. + +The traditional Unix mallocs allow memory to be freed multiple +times; that's probably why this has never been fixed. You can +run configure with the `--without-gnu-malloc' option to use +the C library malloc and avoid the problem. + +F4) I'm running SVR4.2. Why is the line erased every time I type `@'? + +The `@' character is the default `line kill' character in most +versions of System V, including SVR4.2. You can change this +character to whatever you want using `stty'. For example, to +change the line kill character to control-u, type + + stty kill ^U + +where the `^' and `U' can be two separate characters. + +F5) Why does bash report syntax errors when my C News scripts use a + redirection before a subshell command? + +The actual command in question is something like + + < file ( command ) + +According to the grammar given in the POSIX.2 standard, this construct +is, in fact, a syntax error. Redirections may only precede `simple +commands'. A subshell construct such as the above is one of the shell's +`compound commands'. A redirection may only follow a compound command. + +This affects the mechanical transformation of commands that use `cat' +to pipe a file into a command (a favorite Useless-Use-Of-Cat topic on +comp.unix.shell). While most commands of the form + + cat file | command + +can be converted to `< file command', shell control structures such as +loops and subshells require `command < file'. + +The file CWRU/sh-redir-hack in the bash distribution is an +(unofficial) patch to parse.y that will modify the grammar to +support this construct. It will not apply with `patch'; you must +modify parse.y by hand. Note that if you apply this, you must +recompile with -DREDIRECTION_HACK. This introduces a large +number of reduce/reduce conflicts into the shell grammar. + +F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? + +The short answer is that Red Hat screwed up. + +The long answer is that they shipped an /etc/inputrc that only works +for emacs mode editing, and then screwed all the vi users by setting +INPUTRC to /etc/inputrc in /etc/profile. + +The short fix is to do one of the following: remove or rename +/etc/inputrc, set INPUTRC=~/.inputrc in ~/.bashrc (or .bash_profile, +but make sure you export it if you do), remove the assignment to +INPUTRC from /etc/profile, add + + set keymap emacs + +to the beginning of /etc/inputrc, or bracket the key bindings in +/etc/inputrc with these lines + + $if mode=emacs + [...] + $endif + +F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on + HP/UX 11.x? + +HP/UX's support for long double is imperfect at best. + +GCC will support it without problems, but the HP C library functions +like strtold(3) and printf(3) don't actually work with long doubles. +HP implemented a `long_double' type as a 4-element array of 32-bit +ints, and that is what the library functions use. The ANSI C +`long double' type is a 128-bit floating point scalar. + +The easiest fix, until HP fixes things up, is to edit the generated +config.h and #undef the HAVE_LONG_DOUBLE line. After doing that, +the compilation should complete successfully. + +Section G: How can I get bash to do certain common things? + +G1) How can I get bash to read and display eight-bit characters? + +This is a process requiring several steps. + +First, you must ensure that the `physical' data path is a full eight +bits. For xterms, for example, the `vt100' resources `eightBitInput' +and `eightBitOutput' should be set to `true'. + +Once you have set up an eight-bit path, you must tell the kernel and +tty driver to leave the eighth bit of characters alone when processing +keyboard input. Use `stty' to do this: + + stty cs8 -istrip -parenb + +For old BSD-style systems, you can use + + stty pass8 + +You may also need + + stty even odd + +Finally, you need to tell readline that you will be inputting and +displaying eight-bit characters. You use readline variables to do +this. These variables can be set in your .inputrc or using the bash +`bind' builtin. Here's an example using `bind': + + bash$ bind 'set convert-meta off' + bash$ bind 'set meta-flag on' + bash$ bind 'set output-meta on' + +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? + +This is why the `command' and `builtin' builtins exist. The +`command' builtin executes the command supplied as its first +argument, skipping over any function defined with that name. The +`builtin' builtin executes the builtin command given as its first +argument directly. + +For example, to write a function to replace `cd' that writes the +hostname and current directory to an xterm title bar, use +something like the following: + + cd() + { + builtin cd "$@" && xtitle "$HOST: $PWD" + } + +This could also be written using `command' instead of `builtin'; +the version above is marginally more efficient. + +G3) How can I find the value of a shell variable whose name is the value + of another shell variable? + +Versions of Bash newer than Bash-2.0 support this directly. You can use + + ${!var} + +For example, the following sequence of commands will echo `z': + + var1=var2 + var2=z + echo ${!var1} + +For sh compatibility, use the `eval' builtin. The important +thing to remember is that `eval' expands the arguments you give +it again, so you need to quote the parts of the arguments that +you want `eval' to act on. + +For example, this expression prints the value of the last positional +parameter: + + eval echo \"\$\{$#\}\" + +The expansion of the quoted portions of this expression will be +deferred until `eval' runs, while the `$#' will be expanded +before `eval' is executed. In versions of bash later than bash-2.0, + + echo ${!#} + +does the same thing. + +This is not the same thing as ksh93 `nameref' variables, though the syntax +is similar. I may add namerefs in a future bash version. + +G4) How can I make the bash `time' reserved word print timing output that + looks like the output from my system's /usr/bin/time? + +The bash command timing code looks for a variable `TIMEFORMAT' and +uses its value as a format string to decide how to display the +timing statistics. + +The value of TIMEFORMAT is a string with `%' escapes expanded in a +fashion similar in spirit to printf(3). The manual page explains +the meanings of the escape sequences in the format string. + +If TIMEFORMAT is not set, bash acts as if the following assignment had +been performed: + + TIMEFORMAT=$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS' + +The POSIX.2 default time format (used by `time -p command') is + + TIMEFORMAT=$'real %2R\nuser %2U\nsys %2S' + +The BSD /usr/bin/time format can be emulated with: + + TIMEFORMAT=$'\t%1R real\t%1U user\t%1S sys' + +The System V /usr/bin/time format can be emulated with: + + TIMEFORMAT=$'\nreal\t%1R\nuser\t%1U\nsys\t%1S' + +The ksh format can be emulated with: + + TIMEFORMAT=$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS' + +G5) How do I get the current directory into my prompt? + +Bash provides a number of backslash-escape sequences which are expanded +when the prompt string (PS1 or PS2) is displayed. The full list is in +the manual page. + +The \w expansion gives the full pathname of the current directory, with +a tilde (`~') substituted for the current value of $HOME. The \W +expansion gives the basename of the current directory. To put the full +pathname of the current directory into the path without any tilde +subsitution, use $PWD. Here are some examples: + + PS1='\w$ ' # current directory with tilde + PS1='\W$ ' # basename of current directory + PS1='$PWD$ ' # full pathname of current directory + +The single quotes are important in the final example to prevent $PWD from +being expanded when the assignment to PS1 is performed. + +G6) How can I rename "*.foo" to "*.bar"? + +Use the pattern removal functionality described in D3. The following `for' +loop will do the trick: + + for f in *.foo; do + mv $f ${f%foo}bar + done + +G7) How can I translate a filename from uppercase to lowercase? + +The script examples/functions/lowercase, originally written by John DuBois, +will do the trick. The converse is left as an exercise. + +G8) How can I write a filename expansion (globbing) pattern that will match + all files in the current directory except "." and ".."? + +You must have set the `extglob' shell option using `shopt -s extglob' to use +this: + + echo .!(.|) * + +A solution that works without extended globbing is given in the Unix Shell +FAQ, posted periodically to comp.unix.shell. It's a variant of + + echo .[!.]* ..?* * + +(The ..?* catches files with names of three or more characters beginning +with `..') + +Section H: Where do I go from here? + +H1) How do I report bugs in bash, and where should I look for fixes and + advice? + +Use the `bashbug' script to report bugs. It is built and +installed at the same time as bash. It provides a standard +template for reporting a problem and automatically includes +information about your configuration and build environment. + +`bashbug' sends its reports to bug-bash@gnu.org, which +is a large mailing list gatewayed to the usenet newsgroup gnu.bash.bug. + +Bug fixes, answers to questions, and announcements of new releases +are all posted to gnu.bash.bug. Discussions concerning bash features +and problems also take place there. + +To reach the bash maintainers directly, send mail to +bash-maintainers@gnu.org. + +H2) What kind of bash documentation is there? + +First, look in the doc directory in the bash distribution. It should +contain at least the following files: + +bash.1 an extensive, thorough Unix-style manual page +builtins.1 a manual page covering just bash builtin commands +bashref.texi a reference manual in GNU tex`info format +bashref.info an info version of the reference manual +FAQ this file +article.ms text of an article written for The Linux Journal +readline.3 a man page describing readline + +Postscript, HTML, and ASCII files created from the above source are +available in the documentation distribution. + +There is additional documentation available for anonymous FTP from host +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 +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, 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. + +Rocky Bernstein's bash debugger (support is included with bash-4.0) + +H4) What's on the bash `wish list' for future versions? + +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 +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 `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 2010. Never make predictions. + +This document is Copyright 1995-2010 by Chester Ramey. + +Permission is hereby granted, without written agreement and +without license or royalty fees, to use, copy, and distribute +this document for any purpose, provided that the above copyright +notice appears in all copies of this document and that the +contents of this document remain unaltered. |