UNIX for Beginners Questions & Answers

getopts OPTSTRING VARNAME [ARGS...]
where:
OPTSTRING tells getopts which options to expect and where to expect arguments
VARNAME	tells getopts which shell-variable to use for option reporting
ARGS	tells getopts to parse these optional words instead of the positional parameters

# Utility functions: print-as-echo, print-line-with-visual-space.
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }

pl " Results, getopt, s1 -a mystuff x y z:"
./s1 -a mystuff x y z

pl " Results, getopts, s2 -a mystuff x y z:"
./s2 -a mystuff x y z

pl " Code for s1 and s2:"
pe
head -50 s1 s2

$ ./s0

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 3.16.0-7-amd64, x86_64
Distribution        : Debian 8.11 (jessie) 
bash GNU bash 4.3.30

-----
 Results, getopt, s1 -a mystuff x y z:
Got option 'a' with argument 'mystuff'
Remaining args are: <'x' 'y' 'z'>

-----
 Results, getopts, s2 -a mystuff x y z:
Got option 'a' with argument mystuff
Remaining args are: <x y z>

-----
 Code for s1 and s2:

==> s1 <==
#!/bin/bash

#
# Example using getopt (vs builtin getopts) that can also handle long options.
# Another clean example can be found at:
# http://www.bahmanm.com/blogs/command-line-options-how-to-parse-in-bash-using-getopt
#

aflag=n
bflag=n
cargument=

# Parse options. Note that options may be followed by one colon to indicate
# they have a required argument
if ! options=$(getopt -o a:bc: -l along,blong,clong: -- "$@")
then
  # Error, getopt will put out a message for us
  exit 1
fi

set -- $options

while [ $# -gt 0 ]
do
  # Consume next (1st) argument
  case $1 in
    -b|--blong)
    bflag="y" ;;
    # Options with required arguments, an additional shift is required
    -a|--along)
      aargument="$2" ; shift
      echo "Got option 'a' with argument ${aargument}"
    aflag="y" ;;
    -c|--clong)
    cargument="$2" ; shift;;
    (--)
  shift; break;;
  (-*)
echo "$0: error - unrecognized option $1" 1>&2; exit 1;;
(*)
break;;
esac
  # Fetch next argument as 1st
  shift
done

shift $((OPTIND-1))

echo "Remaining args are: <${@}>"

==> s2 <==
#!/bin/bash

while getopts ":da:" opt; do
  case $opt in
    d)
      echo "Entering DEBUG mode"
    ;;
    a)
      echo "Got option 'a' with argument ${OPTARG}"
    ;;
    :)
      echo "Error: option ${OPTARG} requires an argument"
    ;;
    ?)
      echo "Invalid option: ${OPTARG}"
    ;;
  esac
done

shift $((OPTIND-1))

echo "Remaining args are: <${@}>"