How to pass parameters to an alias?

Question

For bash script, I can use "$@" to access arguments. What's the equivalent when I use an alias?

Answer 1

Alias solution

If you're really against using a function per se, you can use:

$ alias wrap_args='f(){ echo before "$@" after;  unset -f f; }; f'
$ wrap_args x y z
before x y z after

You can replace $@ with $1 if you only want the first argument.

Explanation

This creates a temporary function f, which is passed the arguments.

Alias arguments are only passed at the end. Note that f is called at the very end of the alias.

The unset -f removes the function definition as the alias is executed so it doesn't hang around afterwards.

Answer 2

Aliases don't take arguments. They work more or less like simple text replacement, meaning all words after the alias (the ones that look like "arguments" to the alias) just get left at the end of the expanded alias.

For instance, if you were to alias ls to ls -la, then typing ls foo bar would really execute ls -la foo bar on the command line. Which is probably fine in that example, but if foob is an alias to foo | bar, then foob abc def expands to foo | bar abc def, and there's no way to arrange those two words to be used as arguments to the left-hand side of the pipeline.

One might attempt changing the alias to something like foo "$@" | bar or so, but that would expand to foo "$@" | bar abc def and use the positional parameters of the outer context in the expansion of "$@". That's probably not what you want.

If you want to have actual control over how the arguments are interpreted, then you could write a function like so:

my_program_wrapper() {
    local first_arg=$1 \
          second_arg=$2

    shift 2 # get rid of the first two arguments

    # ...

    /path/to/my_program "$@"
}

Answer 3

Adding to the present answers, an important thing to realize about how aliases work is that all the parameters you type after an aliased command will be used literally at the end. So there is no way to use alias for two commands (piped or not), out of which the first should interpret the parameters. To make it clear, here's an example of something that would not work as expected:

alias lsswp="ls -l | grep swp"

(an example inspired by this question) this will always use the output of ls -l performed in the current directory and do a grep on that - so using

lsswp /tmp/

would be equivalent to ls -l | grep swp /tmp/ and not ls -l /tmp/ | grep swp.

For all purposes where the arguments should be used somewhere in the middle, one needs to use a function instead of an alias.

Answer 4

You don't have to do anything, actually; aliases do this automatically. For instance:

$ alias less="less -eirqM"
$ less foo.txt

You will see foo.txt's first page, and less will quit at EOF (-e), searches will be case-insensitive (-i), etc.

Answer 5

I'm answering for csh:

Yes, you can use the parameters in aliases and - as a difference to what has been said above - you can refer to them anywhere in the definition of alias - not only at the end.

Example for tar-gz -ing something:

$ alias tgz "tar cvf - \!:1 | gzip -9 > \!:2.tar.gz"

, where !:1 and !:2 are the parameters you will supply when calling your alias.

Example of use:

    $ ls
    clrcf.dat                             user_comment_2016.06.03_12:51:50.txt  user_comment_2016.06.03_12:54:48.txt
        TEST-wADM.tec                         user_comment_2016.06.03_12:52:04.txt  user_comment_2016.06.03_12:55:13.txt


    $ tgz user* out
    a user_comment_2016.06.03_12:51:50.txt 1K
a user_comment_2016.06.03_12:52:04.txt 1K
a user_comment_2016.06.03_12:54:48.txt 1K
a user_comment_2016.06.03_12:55:13.txt 1K

    $ ls out*
    out.tar.gz

Which effectively means that you used two parameters that you inserted at arbitrary places of the tar command, making of all of it an alias tgz

Answer 6

This example, to pretty print a markdown file in the terminal, is working if the first command of the pipe is able to read from stdin:

alias mdcat='(pandoc | lynx -stdin -dump) <'

So mdcat myfile.md can then be used instead of pandoc myfile.md | lynx -stdin -dump.

This is not exactly answering your question, as it does not make "$@" available in the alias, but it probably answers some real-world usecases for this question.