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09.28.05
Bash Aliases
 By
A.P. Lawrence
Most shells have some provision for aliases. Aliases
can assign default behavior to a command (for example "rm" is
often aliased to "rm -i") or can be used to create new commands
(a typical example is "ll" aliased to be "ls -l").
Aliases are expanded before looking in $PATH. Depending upon
your Bash settings, a "which" for a over-ride alias like "rm"
may show you the commands found in $PATH also:
bash-2.01$ which rm
rm: aliased to rm -i
# a different machine
bash-2.05b$ which rm
alias rm='rm -i'
/bin/rm
To get the second behavior, 'which' itself was aliased :
bash-2.05b$ which which alias which='alias | /usr/bin/which
--tty-only --read-alias --show-dot --show-tilde' /usr/bin/which
Aliases are NOT normally expanded in non-interactive shells, which means that if you use "rm" in a script, you won't get the alias - unless you want yo, in which case you do "shopt -s expand_aliases" before calling it. If you want to be safe, use /bin/rm instead, which can't ever be confused with an alias.
There are other confusing rules for alias expansion; even the man page admits the potential for gross misunderstanding and follows that confession with this:
For almost every purpose, aliases are superseded by shell functions.
You might construe that as an apology of sorts, but while the
maintainers of Bash might fondly hope (and have excellent reasons
for hoping) for that to be true, in fact and in common practise,
aliases continue to be used regularly and I have little doubt
that will remain true for a long, long time.
*Originally published at APLawrence.com
About
the Author:
A.P. Lawrence provides SCO Unix and Linux consulting services http://www.pcunix.com
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