Objective: The alias command can be used to launch any command or a group of commands (inclusive of any options, arguments and redirection) by entering a pre-set string. But how to pass an argument to alias or let an alias handle a variable?
ll‘ to run ‘ls -l‘. This is how you define the alias.
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$ alias ll="ls -l" |
Alias with Arguments
Now, let’s say that you want to list the last two modified files in a specific directory. You could use the following command to list the two latest files based on modification date.
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$ ls -lt /path/to/directory | tail -2 |
To define the above command as an alias which takes in a directory path, we can use the following syntax.
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$ alias last2='function _(){ ls -lt $1 | tail -2; }; _' |
We have to define a function within alias to achieve our goal. Note the use of semicolons after the tail command and after the closing brace. You can run the alias like this.
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$ last2 /path/to/directory |
Alias with Variables
Let’s say you have a variable called BACKUP_DIR that points to a directory. You need to make a tar gzip backup of that directory and you need to touch a file once you are done. To do that, you will need to run:
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$ tar czvf /path/to/backup/backup.tar.gz $BACKUP_DIR ; touch /path/to/backup/last_backup |
To use an alias for the above command, use one of the following syntax. One uses single quotes and another uses double quotes with escape strings.
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$ alias dobackup='tar czvf /path/to/backup/backup.tar.gz $BACKUP_DIR ; touch /path/to/backup/last_backup' |
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$ alias dobackup="tar czvf /path/to/backup/backup.tar.gz \$BACKUP_DIR ; touch /path/to/backup/last_backup" |
After defining the alias, make sure that the variable BACKUP_DIR is not interpreted. The variable should be printed without being interpreted by the shell. You can verify this by running:
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$ alias dobackup alias dobackup='tar czvf /path/to/backup/backup.tar.gz $BACKUP_DIR ; touch /path/to/backup/last_backup' |
If the output is something like the one below (BACKUP_DIR is replaced by “/path/to/backup/directory“, then most probably you did not define the alias properly. Check the quotes and make sure the variables are escaped properly.
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$ alias dobackup alias dobackup='tar czvf /path/to/backup/backup.tar.gz /path/to/backup/directory ; touch /path/to/backup/last_backup' |
Mohamed Ibrahim
ibrahim = { interested_in(unix, linux, android, open_source, reverse_engineering); coding(c, shell, php, python, java, javascript, nodejs, react); plays_on(xbox, ps4); linux_desktop_user(true); }
