Optional option argument with getopts

while getopts "hd:R:" arg; do
  case $arg in
    h)
      echo "usage" 
      ;;
    d)
      dir=$OPTARG
      ;;
    R)
      if [[ $OPTARG =~ ^[0-9]+$ ]];then
        level=$OPTARG
      else
        level=1
      fi
      ;;
    \?)
      echo "WRONG" >&2
      ;;
  esac
done

• level refers to the parameter of -R, dir refers to parameters of -d

• when I input ./count.sh -R 1 -d test/ it works correctly

• when I input ./count.sh -d test/ -R 1 it works correctly

• but I want to have it work when I input ./count.sh -d test/ -R or ./count.sh -R -d test/

This means that I want -R to have a default value and for the sequence of commands to be more flexible.

Solution 1:

Wrong. Actually getopts does support optional arguments! From the bash man page:

If  a  required  argument is not found, and getopts is not silent, 
a question mark (?) is placed in name, OPTARG is unset, and a diagnostic
message is printed.  If getopts is silent, then a colon (:) is placed in name 
and OPTARG is set to the option character found.

When the man page says "silent" it means silent error reporting. To enable it, the first character of optstring needs to be a colon:

while getopts ":hd:R:" arg; do
    # ...rest of iverson's loop should work as posted 
done

Since Bash's getopt does not recognize -- to end the options list, it may not work when -R is the last option, followed by some path argument.

P.S.: Traditionally, getopt.c uses two colons (::) to specify an optional argument. However, the version used by Bash doesn't.

Solution 2:

getopts doesn't really support this; but it's not hard to write your own replacement.

while true; do
    case $1 in
      -R) level=1
            shift
            case $1 in
              *[!0-9]* | "") ;;
              *) level=$1; shift ;;
            esac ;;
        # ... Other options ...
        -*) echo "$0: Unrecognized option $1" >&2
            exit 2;;
        *) break ;;
    esac
done

Solution 3:

This workaround defines 'R' with no argument (no ':'), tests for any argument after the '-R' (manage last option on the command line) and tests if an existing argument starts with a dash.

# No : after R
while getopts "hd:R" arg; do
  case $arg in
  (...)
  R)
    # Check next positional parameter
    eval nextopt=\${$OPTIND}
    # existing or starting with dash?
    if [[ -n $nextopt && $nextopt != -* ]] ; then
      OPTIND=$((OPTIND + 1))
      level=$nextopt
    else
      level=1
    fi
    ;;
  (...)
  esac
done

Solution 4:

I agree with tripleee, getopts does not support optional argument handling.

The compromised solution I have settled on is to use the upper case/lower case combination of the same option flag to differentiate between the option that takes an argument and the other that does not.

Example:

COMMAND_LINE_OPTIONS_HELP='
Command line options:
    -I          Process all the files in the default dir: '`pwd`'/input/
    -i  DIR     Process all the files in the user specified input dir
    -h          Print this help menu

Examples:
    Process all files in the default input dir
        '`basename $0`' -I

    Process all files in the user specified input dir
        '`basename $0`' -i ~/my/input/dir

'

VALID_COMMAND_LINE_OPTIONS="i:Ih"
INPUT_DIR=

while getopts $VALID_COMMAND_LINE_OPTIONS options; do
    #echo "option is " $options
    case $options in
        h)
            echo "$COMMAND_LINE_OPTIONS_HELP"
            exit $E_OPTERROR;
        ;;
        I)
            INPUT_DIR=`pwd`/input
            echo ""
            echo "***************************"
            echo "Use DEFAULT input dir : $INPUT_DIR"
            echo "***************************"
        ;;
        i)
            INPUT_DIR=$OPTARG
            echo ""
            echo "***************************"
            echo "Use USER SPECIFIED input dir : $INPUT_DIR"
            echo "***************************"
        ;;
        \?)
            echo "Usage: `basename $0` -h for help";
            echo "$COMMAND_LINE_OPTIONS_HELP"
            exit $E_OPTERROR;
        ;;
    esac
done