CodeWord: Apokalyptik

This is something that has always annoyed me about bash scripts… The fact that it’s difficult to run

/path/to/script.sh --foo=bar -v -n 10 blah -one='last arg'

So I decided to write up a bash function that let me easily (once the function was complete) access this type of information. And because I like sharing, here it is:

#!/bin/bash
function getopt() {
  var=""
  wantarg=0
  for (( i=1; i< =$#; i+=1 )); do
    lastvar=$var
    var=${!i}
    if [ "$var" = "" ]; then 
        continue 
    fi
    echo \ $var | grep -q -- '='
    if [ $? -eq 0 ]; then
      ## -*param=value
      var=$(echo \ $var | sed -r s/'^[ ]*-*'/''/)
      myvar=${var%=*}
      myval=${var#*=}
      eval "${myvar}"="'$myval'"
    else
      echo \ $var | grep -E -q -- '^[ ]*-'
      if [ $? -eq 0 ]; then
        # -*param$
        var=$(echo \ $var | sed -r s/'^[ ]*-*'/''/)
        eval "${var}"=1
        wantarg=1
      else
        echo \ $var | grep -E -- '^[ ]*-'
        if [ $? -eq 0 ]; then
          # the current one has a dash, so cannot be
          # the argument to the last parameter
          wantarg=0
        fi
        if [ $wantarg -eq 1 ]; then
          # parameter argument
          val=$var
          var=$lastvar
          eval "${var}"="'${val}'"
          wantarg=0
        else
          # parameter
          if [ "${!var}" = "" ]; then
            eval "${var}"=1
          fi
          wantarg=0
        fi
      fi
    fi
  done
}
 
OIFS=$IFS; IFS=$(echo -e "\n"); getopt $@; IFS=$OIFS

now at this point (assuming the above command line parameter and script) I should have access to the following variables: $foo (“bar”) $v (1) $n (10) $blah (1) $one (“last arg”), like so:

OIFS=$IFS; IFS=$(echo -e "\n"); getopt $@; IFS=$OIFS
 
echo -e "
foo:\t$foo
v:\t$v
n:\t$n
blah:\t$blah
one:\t$one
"

You might be curious about this line:

OIFS=$IFS; IFS=$(echo -e "\n"); getopt $@; IFS=$OIFS

IFS is the variable that tells bash how strings are separated (and mastering its use will go a long way towards enhancing your bash scripting skills.) Anyhow, by default IFS=" " which normally is OK, but in our case we dont want "last arg" to be two seperate strings, but one. I cannot put the IFS assignment inside the function because by that point bash has already split the variable, it needs to be done at a level of the script in which $@ has not been touched yet. So I store the current IFS variable in $OIFS (Old IFS) and set IFS to a newline character. After running the function we reassign IFS to what it was beforehand. This is because I dont know what you might be doing with your IFS. There are lots of reasons you might have already assigned it to something else, and I wouldnt want to break your flow. So we do the polite thing.

And in case the above gets munged for some reason you can see the plain text version here: bash-getopt/getopt.sh

Anyways, hope this helps someone out. If not it's still here for me when *I* need it