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Forward arguments in shell

sleeplessbyte profile image Derk-Jan Karrenbeld Originally published at derk-jan.com ・2 min read

Originally published at derk-jan.com. I have recently taken up writing, again and am trying to commit to at least one helpful post each week for the next 52 weeks.

For one of my CLIs, I needed to remove the first argument from the argument list and forward the rest to a next process. In this example, my shell script is called cli_process and given arguments arg1, arg2 and arg3, I want to execute forward_process with arg2 and arg3.

#!/usr/bin/env bash

# Documentation on @
#   https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#index-_0040
# Documentation on shift [n]
#   https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#index-shift
# Why quoting the argument is "necessary":
#   https://stackoverflow.com/questions/4824590/propagate-all-arguments-in-a-bash-shell-script/4824637#4824637

# eats 1 argument
shift 1

# forwards the rest to "forward_process"
forward_process "$@"

Originally posted as a gist, by myself.

Windows

Windows .bat files support a similar token: %*, which is equivalent to $@.
However, the SHIFT command, unlike the bash equivalent shift, doesn't modify this special token. There are various solutions that will attempt to eat the first n parameters, but all of them have edge-cases in which they don't properly work. Should you need this in windows, I recommend you write out the arguments manually %2, %3 (and skip %1).

Here you can find some Windows solutions, but make sure you check the comments underneath each one:

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Discussion

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Heh... if you're someone that implements flag/args in bash, you're familiar with shift because it's how you parse getopt strings.

 

Absolutely! But when I needed to do this, I did not have that knowledge yet. Only needed to drop an argument and pass it on to the next binary :).

Shift is great