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Revision 2 as of 2008-03-02 00:16:06
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Editor: brt48
Comment: by limcore.com woot?
Revision 9 as of 2009-11-03 19:50:20
Size: 2702
Editor: GreyCat
Comment: add POSIX version of the non-getopts example
Deletions are marked like this. Additions are marked like this.
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[[Anchor(faq35)]] <<Anchor(faq35)>>
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    while [[ $1 == -* ]]; do
        case "$1" in
          -h|--help) show_help; exit 0;;
          -v) verbose=1; shift;;
          -f) output_file=$2; shift 2;;
        esac
    done
    # Now all of the remaining arguments are the filenames which followed
    # the optional switches. You can process those with "for i" or "$@".
# Bash
while [[ $1 == -* ]]; do
    case "$1" in
      -h|--help|-\?) show_help; exit 0;;
      -v|--verbose) verbose=1; shift;;
      -f) if (($# > 1)); then
            output_file=$2; shift 2
          else
            printf "%s\n" "-f requires an argument"
            exit 1
          fi ;;
      --) shift; break;;
      -*) echo "invalid option: $1"; show_help; exit 1;;
    esac
done
}}}
Now all of the remaining arguments are the filenames which followed the optional switches. You can process those with `for i` or `"$@"`.

A POSIX version of that same code:
{{{
# POSIX
while true; do
    case "$1" in
      -h|--help|-\?) show_help; exit 0;;
      -v|--verbose) verbose=1; shift;;
      -f) if [ $# -gt 1 ]; then
            output_file=$2; shift 2
          else
            printf "%s\n" "-f requires an argument"
            exit 1
          fi ;;
      --) shift; break;;
      -*) echo "invalid option: $1"; show_help; exit 1;;
      *) break;;
    esac
done
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For more complex/generalized cases, or if you want things like "-xvf" to be handled as three separate flags, you can use getopts. ('''NEVER use getopt(1)!''') For more complex/generalized cases, or if you want things like "-xvf" to be handled as three separate flags, you can use `getopts`. ('''NEVER use getopt(1)!''')
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Here is a simplistic getopts example: Here is a simplistic `getopts` example:
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    x=1  # Avoids an error if we get no options at all.
    while getopts "abcf:g:h:" opt; do
      case "$opt" in
        a) echo "You said a";;
    
b) echo "You said b";;
        c) echo "You said c";;
    
f) echo "You said f, with argument $OPTARG";;
        g) echo "You said g, with argument $OPTARG";;
        h) echo "You said h, with argument $OPTARG";;
      esac
    
x=$OPTIND
    done
    
shift $((x-1))
    echo "Left overs: $@"
# POSIX
x=1         # Avoids an error if we get no options at all.
while getopts "abcf:g:h:" opt; do
  case "$opt" in
    a) echo "You said a";;
b) echo "You said b";;
    c) echo "You said c";;
f) echo "You said f, with argument $OPTARG";;
    g) echo "You said g, with argument $OPTARG";;
    h) echo "You said h, with argument $OPTARG";;
  esac
x=$OPTIND
done
shift $(($x-1))
echo "Left overs: $@"
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If your prefer to check options with IFs quickly then:
If you prefer to check options with `if` statements, then a function like this one may be useful:
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function HaveOpt {
  needle=$1
# Bash
HaveOpt() {
  local needle=$1
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      --) return 1; # stop now, since -- by convention is end of option arguments       --) return 1; # by convention, -- is end of options
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  return 1;   return 1
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if HaveOpt --quick "$@"; then echo "Option quick is set"; fi
}}}
and it will work if script is run as:
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May be useful.
Use if like:
HaveOpt --quick $* && echo "Option quick is set"
 * YES: ./script --quick
 * YES: ./script -other --quick
but will stop on first argument with no "-" in front (or on --):
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and it will work if script is run as:
YES: ./script --quick
YES: ./script -other --quick
but will stop on first no minus argument (or --)
NO: ./script -bar foo --quick
NO: ./script -bar -- --quick

}}}
 * NO: ./script -bar foo --quick
 * NO: ./script -bar -- --quick
Of course, this approach (iterating over the argument list every time you want to check for one) is far less efficient than just iterating once and setting flag variables.

How can I handle command-line arguments to my script easily?

Well, that depends a great deal on what you want to do with them. Here's a general template that might help for the simple cases:

# Bash
while [[ $1 == -* ]]; do
    case "$1" in
      -h|--help|-\?) show_help; exit 0;;
      -v|--verbose) verbose=1; shift;;
      -f) if (($# > 1)); then
            output_file=$2; shift 2
          else 
            printf "%s\n" "-f requires an argument"
            exit 1
          fi ;;
      --) shift; break;;
      -*) echo "invalid option: $1"; show_help; exit 1;;
    esac
done

Now all of the remaining arguments are the filenames which followed the optional switches. You can process those with for i or "$@".

A POSIX version of that same code:

# POSIX
while true; do
    case "$1" in
      -h|--help|-\?) show_help; exit 0;;
      -v|--verbose) verbose=1; shift;;
      -f) if [ $# -gt 1 ]; then
            output_file=$2; shift 2
          else 
            printf "%s\n" "-f requires an argument"
            exit 1
          fi ;;
      --) shift; break;;
      -*) echo "invalid option: $1"; show_help; exit 1;;
      *)  break;;
    esac
done

For more complex/generalized cases, or if you want things like "-xvf" to be handled as three separate flags, you can use getopts. (NEVER use getopt(1)!)

Here is a simplistic getopts example:

# POSIX
x=1         # Avoids an error if we get no options at all.
while getopts "abcf:g:h:" opt; do
  case "$opt" in
    a) echo "You said a";;
    b) echo "You said b";;
    c) echo "You said c";;
    f) echo "You said f, with argument $OPTARG";;
    g) echo "You said g, with argument $OPTARG";;
    h) echo "You said h, with argument $OPTARG";;
  esac
  x=$OPTIND
done
shift $(($x-1))
echo "Left overs: $@"

If you prefer to check options with if statements, then a function like this one may be useful:

# Bash
HaveOpt() {
  local needle=$1
  shift
  while [[ $1 == -* ]]; do
    case "$1" in
      --) return 1; # by convention, -- is end of options
      $needle) return 0;;
    esac
    shift
  done
  return 1
}
if HaveOpt --quick "$@"; then echo "Option quick is set"; fi

and it will work if script is run as:

  • YES: ./script --quick
  • YES: ./script -other --quick

but will stop on first argument with no "-" in front (or on --):

  • NO: ./script -bar foo --quick
  • NO: ./script -bar -- --quick

Of course, this approach (iterating over the argument list every time you want to check for one) is far less efficient than just iterating once and setting flag variables.

BashFAQ/035 (last edited 2024-02-26 07:51:38 by larryv)