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Shell Aliases

Aliases are parameterless macros that are recognized only as the first word of the command string. They allow only simple substitution.  The shell maintains a list of aliases that may be set and unset with the `alias' and `unalias' built-in commands.  Aliases don't allow for control flow, command-line arguments, or other features that makes the command line so useful. For any more or less complex case, shell functions are preferred over aliases.

Additionally, the rules surrounding alias expansion are a bit tricky, enough so that the bash(1) man page recommends "To be safe, always put alias definitions on a separate line, and do not use alias[es] in compound commands."

The syntax for creating aliases for the Korn shell is alias name=value. This creates an alias for the alias command: alias a=alias

The Korn shell comes with a default set of predefined aliases. To display the list, type alias and press Return:

autoload=typeset -fu
false=let Ø
functions=typeset -f
hash=alias -t -
history=fc -l
integer=typeset -i
nohup=nohup
r=fc -e -
stop=kill -STOP
suspend=kill -STOP $$
true=:
type=whence -v

The first word of each simple command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The alias name and the replacement text may contain any valid shell input, including shell metacharacters, with the exception that the alias name may not contain `='. The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias `ls' to `"ls -F"', for instance, and Bash does not try to recursively expand the replacement text. If the last character of the alias value is a space or tab character, then the next command word following the alias is also checked for alias expansion.

Aliases are created and listed with the `alias' command, and removed with the `unalias' command.

There is no mechanism for using arguments in the replacement text, as in `csh'. If arguments are needed, a shell function should be used

Aliases are not expanded when the shell is not interactive, unless the `expand_aliases' shell option is set using `shopt' (*note Bash Builtins::).

The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads at least one complete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an issue when functions are executed. Aliases are expanded when a function definition is read, not when the function is executed, because a function definition is itself a compound command. As a consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use `alias' in compound commands.

Warning Aliases are very useful things, but I hope that you will find functions at least as interesting and even more useful. You should be very careful replacing a standard command with an alias or a function. It's too easy to really hurt yourself by trying to execute your alias when it doesn't exist. Imagine the difference between doing this:

$ alias rm='rm -i'
$ cd ~/scratch
$ rm *  # here the rm alias catches you and interactively
     # deletes the contents of your current directory

and then later in the same session doing this:

$ su -
# cd /tmp
# rm # here the rm alias no longer exists, and you whack
   # a bunch of stuff out of /tmp

Good luck !

Dr. Nikolai Bezroukov

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News

Jamie's Shell Stuff

~/myenv/bash.aliases :

alias cls=clear
 
alias hist=history
alias !='history | tail -15'
 
alias l='ls -alF'
alias ll='ls -alF'
alias dir='ls -la'
alias la='ls -Fa'
 
alias md='mkdir -p'
alias rd=rmdir
alias ..='cd ..'
alias ...='cd ../..'
alias +='pushd .' 

[X-Unix] Quoting in bash aliases

Eugene Lee list-themacintoshguy at fsck.net
Thu Feb 19 04:47:35 PST 2004

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---

On Thu, Feb 19, 2004 at 01:28:32PM +0100, Kirk McElhearn wrote:
: 
: The following command replaces Mac line breaks with Unix line breaks:
: 
: perl -pi -e 's/\r\n?/\n/g'
: 
: I'd like to make an alias in bash, something like:
: 
: alias rplc='perl -pi -e 's/\r\n?/\n/g''
: 
: But the above doesn't work. I assume it has something to do with quoting.
: I've tried double-quotes, escaping the quotes in the perl string and more.
: 
: Can anyone tell me how this needs to be quoted to work correctly?

This worked for me at the command line:

	$ alias rplc="perl -pi -e 's/\r\n?/\n/g'"

Once the alias was created, this is how /bin/bash stored it:

	$ alias
	alias rplc='perl -pi -e '\''s/\r\n?/\n/g'\'''

However, you can use the rules of quoting to create an alias that is
easier to type and easier to read:

	$ alias rplc='perl -pi -e "s/\r\n?/\n/g"'


-- 
Eugene Lee
http://www.coxar.pwp.blueyonder.co.uk/

Useful Bash Aliases and Other Stuff

OneOfOne - Tips-Bash Aliases

bash.aliases [Homepage von Robert Kehl]

alias md=mkdir
alias rd=rmdir
alias su-='sudo su -'

# inventions

alias ghist='history | grep '
alias lf='find -type f | sort '
alias load='cat /proc/loadavg '
alias meminfo='cat /proc/meminfo '

# logs
alias mylogs='sudo tail -f /var/log/{apache2/*log,squid/access.log,otrs.log,exim*log,messages}'
alias mylogs2='sudo tail -f /var/log/{syslog,daemon.log,user.log,router.log}'
# OTRS
alias vio='vi /opt/otrs/Kernel/{Config/Defaults.pm,Config.pm}'

# Kalendar
alias kal='clear;echo -n "Heutiges Datum: ";date;echo;cal -3m'

# switch off
alias s &>/dev/null && unalias s
alias p &>/dev/null && unalias p

Recommended Links

Advanced Bash-Scripting Guide - Chapter 24. Aliases

Files, Users, and Shell Customization

Functions and aliases in bash LG #53

The shell maintains a list of aliases that may be set and unset with the alias and unalias builtin commands.

The first word of each command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text of the alias. The alias name and the replacement text may contain any valid shell input, including shell metacharacters, with the exception that the alias name may not contain =. The first word of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second time. This means that one may alias ls to "ls -F", for instance, and Bash does not try to recursively expand the replacement text. If the last character of the alias value is a space or tab character, then the next command word following the alias is also checked for alias expansion.

Aliases are created and listed with the alias command, and removed with the unalias command.

There is no mechanism for using arguments in the replacement text, as in csh. If arguments are needed, a shell function should be used (see section Shell Functions).

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see section Bash Builtin Commands).

The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads at least one complete line of input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed. Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an issue when functions are executed. Aliases are expanded when the function definition is read, not when the function is executed, because a function definition is itself a compound command. As a consequence, aliases defined in a function are not available until after that function is executed. To be safe, always put alias definitions on a separate line, and do not use alias in compound commands.

Note that for almost every purpose, aliases are superseded by shell functions.

Alias Builtins

alias

alias [-p] [name[=value] ...]

Without arguments or with the `-p' option, alias prints the list of aliases on the standard output in a form that allows them to be reused as input. If arguments are supplied, an alias is defined for each name whose value is given. If no value is given, the name and value of the alias is printed.

unalias

unalias [-a] [name ... ]

Remove each name from the list of aliases. If `-a' is supplied, all aliases are removed.

Last modified: March 15, 2008