Working more productively with bash 2.x

• Overview and introduction
• Tips and Tricks
• Programmable completion
  • Introduction
  • Standard completion
  • Download
  • Installation
  • Getting started
  • Implementation
  • Bug fixes and enhancements
  • Contacting me

Overview and Introduction

bash is a shell, a.k.a. command language interpreter for modern computers. It is Bourne shell (sh) compatible and incorporates useful features from the Korn shell (ksh) and C shell (csh). It conforms to the IEEE POSIX P1003.2/ISO 9945.2 Shell and Tools standard.

Some of bash's features are, in no particular order: editing and completion; history and command re-entry; job control; shell functions and aliases; arrays; arithmetic; ANSI C quoting; tilde expansion; brace expansion; substring capabilities; indirect variable expansion; expanded I/O capabilities; control of built-in commands; help; directory stack; POSIX mode; internationalisation; command timing.

bash is the default shell on all popular Linux distributions. For this reason, it's widely used, but rarely to anything like its full potential.

bash is, perhaps, the Linux program you use the most at work, yet how much are you really getting out of it? If you would like to enhance your productivity by reducing the amount of keystrokes you type on a given day, this document is for you.

bash Tips and Tricks

• shell variables

  $CDPATH

  This is a little known and very underrated shell variable. CDPATH does for the cd built-in what PATH does for executables. By setting this wisely, you can cut down on the number of key-strokes you enter per day.

  Try this:

  $ export CDPATH=.:~:~/docs:~/src:~/src/ops/docs:/mnt:/usr/src/redhat:/usr/src/redhat/RPMS:/usr/src:/usr/lib:/usr/local:/software:/software/redhat

  Using this, cd i386 would likely take you to /usr/src/redhat/RPMS/i386 on a Red Hat Linux system.

  $HISTIGNORE

  Set this to to avoid having consecutive duplicate commands and other not so useful information appended to the history list. This will cut down on hitting the up arrow endlessly to get to the command before the one you just entered twenty times. It will also avoid filling a large percentage of your history list with useless commands.

  Try this:

  $ export HISTIGNORE="&:ls:ls *:mutt:[bf]g:exit"

  Using this, consecutive duplicate commands, invocations of ls, executions of the mutt mail client without any additional parameters, plus calls to the bg, fg and exit built-ins will not be appended to the history list.

  $MAILPATH

  bash will warn you of new mail in any folder appended to MAILPATH. This is very handy if you use a tool like procmail to presort your e-mail into folders.

  Try adding the following to your ~/.bash_profile to be notified when any new mail is deposited in any mailbox under ~/Mail.

  	MAILPATH=/var/spool/mail/$USER
  	for i in `echo ~/Mail/[^.]*`
  	do
  		MAILPATH=$MAILPATH:$i
  	done
  	export MAILPATH
  	unset i
  	

  If you use mutt and many of those folders don't receive automatically filtered mail, you may prefer to have bash alert you only when new e-mail arrives in a folder that you also track in mutt.

  In that case, try something like the following in your ~/.bash_profile:

  	export `perl -ne 's/^mailboxes /MAILPATH=/ && tr/ /:/ && print && exit' < ~/.muttrc`
  	

  $TMOUT

  If you set this to a value greater than zero, bash will terminate after this number of seconds have elapsed if no input arrives.

  This setting is useful in root's environment to reduce the potential security risk of someone forgetting to log out as the superuser.

• set options

  ignoreeof

  Ordinarily, issuing Ctrl-D at the prompt will log you out of an interactive shell. This can be annoying if you regularly need to type Ctrl-D in other situations, for example, when trying to disconnect from a Telnet session. In such a situation, hitting Ctrl-D once too often will close your shell, which can be very frustrating. This option disables the use of Ctrl-D to exit the shell.

• shopt options

  You can set each of the options below with shopt -s <option>.

  cdspell

  This will correct minor spelling errors in a cd command, so that instances of transposed characters, missing characters and extra characters are corrected without the need for retyping.

  cmdhist

  This is very much a matter of taste. Defining this will cause multi-line commands to be appended to your bash history as a single line command. This makes for easy command editing.

  dotglob

  This one allows files beginning with a dot ('.') to be returned in the results of path-name expansion.

  extglob

  This will give you ksh-88 egrep-style extended pattern matching or, in other words, turbo-charged pattern matching within bash. The available operators are:

  ?(pattern-list)

  Matches zero or one occurrence of the given patterns

  *(pattern-list)

  Matches zero or more occurrences of the given patterns

  +(pattern-list)

  Matches one or more occurrences of the given patterns

  @(pattern-list)

  Matches exactly one of the given patterns

  !(pattern-list)

  Matches anything except one of the given patterns

  Here's an example. Say, you wanted to install all RPMs in a given directory, except those built for the noarch architecture. You might use something like this:

  rpm -Uvh /usr/src/RPMS/!(*noarch*)

  These expressions can be nested, too, so if you wanted a directory listing of all non PDF and PostScript files in the current directory, you might do this:

  ls -lad !(*.p?(df|s))

The readline library is used by bash and many other programs to read a line from the terminal, allowing the user to edit the line with standard Emacs editing keys.

• set show-all-if-ambiguous on

  If you have this in your /etc/inputrc or ~/.inputrc, you will no longer have to hit the <Tab> key twice to produce a list of all possible completions. A single <Tab> will suffice. This setting is highly recommended.

• set visible-stats on

  Adding this to your /etc/inputrc or ~/.inputrc will result in a character being appended to any file-names returned by completion, in much the same way as ls -F works.

• If you're a fan of vi as opposed to Emacs, you might prefer to operate bash in vi editing mode. Being a GNU program, bash uses Emacs bindings unless you specify otherwise.

  Set the following in your /etc/inputrc or ~/.inputrc:

  set editing-mode vi
  set keymap vi

  and this in your /etc/bashrc or ~/.bashrc:

  set -o vi

A relatively new feature in bash is programmable completion, which has been available since the beta version of 2.04. Programmable completion will be familiar to you if you are a zsh user. It also exists, albeit in a much less usable form, in tcsh.

It's much easier to demonstrate programmable completion than it is to explain it, so I suggest installing one of the files below and trying it out. If you don't like it, you can always disable it for a particular command, disable it completely, or remove it from your system. It can be installed and removed very cleanly, so you shouldn't be wary of giving it a whirl.

Standard completion

Programmable completion indefinitely extends the type of completion you can perform.

Download

The following files are available for download. All of them are made available under the GNU General Public License.

File	Type
bash-completion-20020507.tar.gz	tarred and gzipped source for bash 2.05 and later
Changelog	CVS change log of bash_completion
bash-completion-20020507-1.noarch.rpm	Binary RPM for bash 2.05-12 and later
bash-completion-20020507-1.src.rpm	Source RPM for bash 2.05-12 and later
bash-2.05a-service_completion.patch	Patch (release 20020207) to bash 2.05a to add service completion
bash-2.05a-54.i386.rpm	Binary RPM of bash 2.05a with above patch applied
bash-doc-2.05a-54.i386.rpm	Binary RPM of bash 2.05a documentation
bash-2.05a-54.src.rpm	Source RPM of bash 2.05a with above patch applied
bash-2.05-group_completion.patch	Patch to bash 2.05 to add group completion
bash-2.05-service_completion.patch	Patch to bash 2.05 to add service completion (requires prior application of the group completion patch)
bash-2.05-51.i386.rpm	Binary RPM of bash 2.05 with above patches applied
bash-doc-2.05-51.i386.rpm	Binary RPM of bash 2.05 documentation
bash-2.05-51.src.rpm	Source RPM of bash 2.05 with above patches applied

Installation

Afterwards, you will find you have a new file on your system, /etc/bash_completion. Assuming you didn't add the --noscripts switch to rpm when you installed, the post-installation of the RPM will have modified your /etc/bashrc to contain the following chunk of code:

# START bash completion -- do not remove this line
bash=${BASH_VERSION%.*}; bmajor=${bash%.*}; bminor=${bash#*.}
if [ "$PS1" ] && [ $bmajor -eq 2 ] && [ $bminor '>' 04 ] \
   && [ -f /etc/bash_completion ]; then # interactive shell
        # Source completion code
        . /etc/bash_completion
fi
unset bash bmajor bminor
# END bash completion -- do not remove this line

If you are installing the source file, either gunzip or bunzip2 it, put it somewhere on your system and source it from either /etc/bashrc or ~/.bashrc. If you are putting it somewhere other than /etc/bash_completion, you will need to edit the top of the file to make $BASH_COMPLETION point to the correct location.

The line you need to adjust is this one:

[ -z "$BASH_COMPLETION" ] && declare -r BASH_COMPLETION=/etc/bash_completion

To get acquainted with programmable completion, it's probably best to just type some of these commands and then hit <Tab> at various positions along the command line. Many commands complete on different things, depending on the position and context of the token on the command line. This screenshot may help you better envisage how completion works in practice.

If you're a sysadmin type, you'll find ssh completion particularly useful, since this completes hostnames based on the contents of your known_hosts files. Also, if you NFS mount a lot of hosts, try mount hostname:<Tab>.

Software engineers will perhaps find p4 and cvs completion useful.

Implementation

Although I offer a source patch to both bash 2.05 and 2.05a to add the feature of service completion, this is currently not used by the bash completion code. It's thus unnecessary to apply this patch unless you want to want to write your own completion definitions that use it.

Bug fixes and enhancements

If you want to be informed as soon as a new version of the code is released, please subscribe to release announcements.

Contacting me

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