Handling parameters into bash scripts

optionize.sh

#!/bin/bash
#
# Copyright (C) 2007 kace
# http://bsdpants.blogspot.de/2007/02/option-ize-your-shell-scripts.html

readonly USAGE='usage: '`basename $0`' [-13ds] [-o out-file] filename'

snmpver=2c
sync=0
debug=0

while [[ ${1:0:1} = '-' ]] ; do
  N=1
  L=${#1}
  while [[ $N -lt $L ]] ; do
    case ${1:$N:1} in
       'd') debug=1 ;;
       's') sync=1 ;;
       '1') snmpver=1 ;;
       '3') snmpver=3 ;;
       'o') if [[ $N -ne $(($L-1)) || ! -n ${2} ]] ; then
              echo $USAGE
              exit 1
            fi
            outfile=${2}
            shift ;;
       *) echo $USAGE
          exit 1 ;;
    esac
    N=$(($N+1))
  done
  shift
done

if [[ ! -n ${1} ]] ; then
  echo $USAGE
  exit 1
fi

infile=$1
echo -n "snmpver:$snmpver debug:$debug sync:$sync "
echo "outfile:$outfile infile:$infile"

usage_example

$ optionize.bsh
usage: optionize.bsh [-13ds] [-o ] filename
$ #that last argument _is_ required
$
$ optionize.bsh blah
snmpver:2c debug:0 sync:0 outfile: infile:blah
$ #defaults
$
$ optionize.bsh -s1 -o yada blah
snmpver:1 debug:0 sync:1 outfile:yada infile:blah
$ #blobs are fine
$
$ optionize.bsh -sd1 -o yada -3 blah
snmpver:3 debug:1 sync:1 outfile:yada infile:blah
$ #last option on the command line overrides any previous
$
$ optionize.bsh -s -d -d1o yada -3o Yadaya blah
snmpver:3 debug:1 sync:1 outfile:Yadaya infile:blah
$ #options requiring arg.s can be in a blob, but ...
$
$ optionize.bsh -d -so1 yada blah
usage: optionize.bsh [-13ds] [-o ] filename
$ # ... not in the middle of a blob, obviously.