Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
echo
if [ TRUE ]
then
alias rr="ls −l"
echo "Trying aliased \"rr\" within if/then statement:"
rr /usr/X11R6/bin/mk* #* Error message results!
# Aliases not expanded within compound statements.
echo "However, previously expanded alias still recognized:"
ll /usr/X11R6/bin/mk*
fi
echo
count=0
while [ $count −lt 3 ]
do
alias rrr="ls −l"
echo "Trying aliased \"rrr\" within \"while\" loop:"
rrr /usr/X11R6/bin/mk*
let count+=1
done
echo; echo
#* Alias will not expand here either.
# alias.sh: line 57: rrr: command not found
alias xyz='cat $0' # Script lists itself.
# Note strong quotes.
xyz
# This seems to work,
#+ although the Bash documentation suggests that it shouldn't.
#
# However, as Steve Jacobson points out,
#+ the "$0" parameter expands immediately upon declaration of the alias.
exit 0
The unalias command removes a previously set alias.
Example 24−2. unalias: Setting and unsetting an alias
#!/bin/bash
shopt −s expand_aliases # Enables alias expansion.
alias llm='ls −al | more'
llm
echo
unalias llm
# Unset alias.
llm
# Error message results, since 'llm' no longer recognized.
exit 0
bash$ ./unalias.sh
total 6
drwxrwxr−x 2 bozo bozo 3072 Feb 6 14:04 .
Chapter 24. Aliases 287