Variable arguments to a shell script

Question

I would like to have my script accepting variable arguments. How do I check for them individually?

For example

./myscript arg1 arg2 arg3 arg4

 or 

./myscript arg4 arg2 arg3

The arguments can be any number and in any order. I would like to check if arg4 string is present or not irrespective of the argument numbers.

How do I do that?

Thanks,

Are these args fixed strings (similar to `--help`, `--version`, etc.) or are they "anything"? — sarnold, Mar 30 '12 at 23:43
Duplicate, http://stackoverflow.com/questions/255898/how-to-iterate-over-arguments-in-bash-script, http://stackoverflow.com/questions/4528292/passing-multiple-arguments-to-a-unix-shell-script — moodywoody, Mar 30 '12 at 23:45
Yeah. I'm passing few flags as arguments to the script not necessarily in fixed numbers. — Kitcha, Mar 30 '12 at 23:46

score 5 · Accepted Answer · answered Mar 30 '12 at 23:52

The safest way — the way that handles all possibilities of whitespace in arguments, and so on — is to write an explicit loop:

arg4_is_an_argument=''
for arg in "$@" ; do
    if [[ "$arg" = 'arg4' ]] ; then
        arg4_is_an_argument=1
    fi
done
if [[ "$arg4_is_an_argument" ]] ; then
    : the argument was present
else
    : the argument was not present
fi

If you're certain your arguments won't contain spaces — or at least, if you're not particularly worried about that case — then you can shorten that to:

if [[ " $* " == *' arg4 '* ]] ; fi
    : the argument was almost certainly present
else
    : the argument was not present
fi

chbrown · Answer 2 · 2017-04-03T23:17:12.113

This is playing fast and loose with the typical interpretation of command line "arguments", but I start most of my bash scripts with the following, as an easy way to add --help support:

if [[ "$@" =~ --help ]]; then
  echo 'So, lemme tell you how to work this here script...'
  exit
fi

The main drawback is that this will also be triggered by arguments like request--help.log, --no--help, etc. (not just --help, which might be a requirement for your solution).

To apply this method in your case, you would write something like:

[[ "$@" =~ arg4 ]] && echo "Ahoy, arg4 sighted!"

Bonus! If your script requires at least one command line argument, you can similarly trigger a help message when no arguments are supplied:

if [[ "${@---help}" =~ --help ]]; then
  echo 'Ok first yer gonna need to find a file...'
  exit 1
fi

which uses the empty-variable-substitution syntax ${VAR-default} to hallucinate a --help argument if absolutely no arguments were given.

score 0 · Answer 3 · edited Jul 22 '12 at 13:05

0

maybe this can help.

#!/bin/bash
# this is myscript.sh

[ `echo $* | grep arg4` ] && echo true || echo false

edited Jul 22 '12 at 13:05

Peter DeWeese

18,141
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answered Mar 31 '12 at 09:28

Umae

445
2
5

Variable arguments to a shell script

3 Answers3