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Aliases

You use the

alias command to create another name for a command. The

alias command operates like a macro that expands to the command it represents. The alias does not literally replace the name of the command; it simply gives another name to that command. An

alias command begins with the keyword

alias and the new name for the command, followed by an equal sign and the command the alias will reference.

In the next example,

list becomes another name for the

ls command:

$ alias list=ls
$ ls
mydata today
$ list
mydata today
$

Aliasing Commands and Options

You can also use an alias to substitute for a command and its option, but you need to enclose both the command and the option within single quotes. Any command you alias that contains spaces must be enclosed in single quotes. In the next example, the alias

lss references the

ls command with its

-s option, and the alias

lsa references the

ls command with the

-F option.

ls with the

-s option lists files and their sizes in blocks, and the

ls with the

-F option places a slash after directory names. Notice how single quotes enclose the command and its option.

$ alias lss='ls -s'
$ lss
mydata 14   today  6   reports  1
$ alias lsa='ls -F'
$ lsa
mydata today reports/
$

Aliases are helpful for simplifying complex operations. In the next example,

listlong becomes another name for the

ls command, with the

-l option for the long format listing all file information, as well as the

-h option for using human readable format for file sizes. Be sure to encase the command and its arguments within single quotes so they are taken as one argument and not parsed by the shell.

$ alias listlong='ls -lh'
$ listlong
-rw-r--r--    1 root   root   51K  Sep  18  2003 mydata
-rw-r--r--    1 root   root   16K  Sep  27  2003 today

Aliasing Commands and Arguments

You may often use an alias to include a command name with an argument. If you execute a command that has an argument with a complex combination of special characters on a regular basis, you may want to alias it. For example, suppose you often list just your source code and object code files—those files ending in either a .c or .o. You would need to use as an argument for

ls a combination of special characters such as

*.[co] . Instead, you could alias

ls with the

.[co] argument, giving it a simple name. In the next example, the user creates an alias called

lsc for the command

ls.[co] :

$ alias lsc='ls *.[co]'
$ lsc
main.c main.o lib.c lib.o

Aliasing Commands

You can also use the name of a command as an alias. This can be helpful in cases where you should use a command only with a specific option. In the case of the

rm ,

cp , and

mv commands, the

-i option should always be used to ensure an existing file is not overwritten. Instead of constantly being careful to use the

-i option each time you use one of these commands, the command name can be aliased to include the option. In the next example, the

rm ,

cp , and

mv commands have been aliased to include the

-i option:

$ alias rm='rm -i'
$ alias mv='mv -i'
$ alias cp='cp -i'

The

alias command by itself provides a list of all aliases that have been defined, showing the commands they represent. You can remove an alias by using the

unalias command. In the next example, the user lists the current aliases and then removes the

lsa alias:

$ alias
lsa=ls -F
list=ls
rm=rm -i
$ unalias lsa