Advanced Bash−Scripting Guide

Chapter 24. Aliases
A Bash alias is essentially nothing more than a keyboard shortcut, an abbreviation, a means of avoiding
typing a long command sequence. If, for example, we include alias lm="ls −l | more" in the ~/.bashrc
file, then each lm typed at the command line will automatically be replaced by a ls −l | more. This can save a
great deal of typing at the command line and avoid having to remember complex combinations of commands
and options. Setting alias rm="rm −i" (interactive mode delete) may save a good deal of grief, since it can
prevent inadvertently losing important files.
In a script, aliases have very limited usefulness. It would be quite nice if aliases could assume some of the
functionality of the C preprocessor, such as macro expansion, but unfortunately Bash does not expand
arguments within the alias body. [55] Moreover, a script fails to expand an alias itself within "compound
constructs", such as if/then statements, loops, and functions. An added limitation is that an alias will not
expand recursively. Almost invariably, whatever we would like an alias to do could be accomplished much
more effectively with a function.
Example 24−1. Aliases within a script
#!/bin/bash
# Invoke with command line parameter to exercise last section of this script.
shopt −s expand_aliases
# Must set this option, else script will not expand aliases.
# First, some fun.
alias Jesse_James='echo "\"Alias Jesse James\" was a 1959 comedy starring Bob Hope."'
Jesse_James
echo; echo; echo;
alias ll="ls −l"
# May use either single (') or double (") quotes to define an alias.
echo "Trying aliased \"ll\":"
ll /usr/X11R6/bin/mk* #* Alias works.
echo
directory=/usr/X11R6/bin/
prefix=mk* # See if wild−card causes problems.
echo "Variables \"directory\" + \"prefix\" = $directory$prefix"
echo
alias lll="ls −l $directory$prefix"
echo "Trying aliased \"lll\":"
lll
# Long listing of all files in /usr/X11R6/bin stating with mk.
# Alias handles concatenated variables, including wild−card o.k.
TRUE=1
Chapter 24. Aliases 286