parsing parameters in shell script

Question

I have a myscript.sh which starts like this:

#!/usr/bin/env bash
set -e

usage(){
  echo "Show Usage ... Blah blah"
  exit 1
}

if [ $# = 0 ]; then
  usage;
fi

while true; do
  case "$1" in
    -l | --build-lib ) BUILD_LIB=true; 
    --other-option ) OTHER_OPTION=$2; shift; shift;;
    -h | --help ) usage; shift;;
    * ) break ;;
  esac
done

# I do my thing here ....
echo "Do my thing"

I am not sure if this is the best way to parse the parameters but so far I have a problem. I am not correctly breaking/failing when the user passes wrong or unknown parameters. How can I address this correctly?

for example I want to avoid calls like:

$ ./myscript.sh unknownParameter

Barmar · Accepted Answer · 2013-03-22 08:43:24Z

3

You need to exit when an incorrect option is given, not just break out of the loop. Easiest way is to call your usage function.

while [ $# -gt 0 ]; do
  case "$1" in
    -l | --build-lib ) BUILD_LIB=tru ;;
    --xcode-dev-path ) XCODE_DEV_PATH=${2%/}; shift ;;
    -h | --help ) usage;;
    * ) usage ;;
  esac
  shift
done

edited Mar 22, 2013 at 8:43

answered Mar 14, 2013 at 2:00

Barmar

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5 Comments

nacho4d Over a year ago

I see that you are using one shitf;; less than me after checking each parameter. How come this is posible? I thought shift was needed to go to the next parameter. - I am kind of lost in shell.

Barmar Over a year ago

I added shift at the bottom of the loop. You always need to shift after each arg, so it's redundant to put that one in each case.

nacho4d Over a year ago

This didn't work as expected. Indeed, I can now avoid calls like $ ./myscript.sh unknownParameter but now I cannot even pass correct parameters like $ ./myscript.sh -l since *) is apparently always reached :(

Barmar Over a year ago

I fixed the missing ;; after the -h case, and changed the while condition so the loop will exit. Does that help? Why aren't you using getopt, anyway?

nacho4d Over a year ago

It worked! Thank you very much. I guess I should learn how to use getopt for proper argument handling.

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