lang:bash:getopts

About

getopts is a command line utility used to parse positional parameters and short option only.

You may want to use getopt that handle positional parameters as only short/single letter option are supported.

ie d is valid but not de

Example

p, d and f are the options. The script usage is:

script.sh -p valuep -d valued -f

The implementations

while getopts "p:d:" option
do
   case "$option" in
      p)   VARIABLE_FOR_P="${OPTARG}";;
      d)   VARIABLE_FOR_D="${OPTARG}";;
      ?)   echo -e "Usage";;
      *)   echo -e "option ${OPTARG} unknown. Usage:\n" ; exit 1 ;;
   esac
done

where:

Bash - Case

Bonus: Prompt for parameters is some required parameters are missing

if [[ -z "$VARIABLE_FOR_P" ]]; then
	echo "VARIABLE_FOR_P:"
	read VARIABLE_FOR_P
        # Test if null
	[[ "${VARIABLE_FOR_P:?The parameter is null sorry}" ]]
fi

Syntax

getopts optstring name [args]

where:

optstring contains the option characters to be recognized;
- If the first character of optstring is a colon, silent error reporting is used.
- if a character is followed by a colon :, the option is expected to have an argument, which should be separated from it by white space.
- The colon and question mark characters may not be used as option characters.
args the positional parameters to parse. if not given parses the argument of the script

Process

Each time it is invoked, getopts set the following variable:

name. Name refers to the next option (name is initialized if it does not exist)
OPTIND. Optind refers to a variable containing the index of the next argument to be processed. OPTIND is initialized to 1 each time the shell or a shell script is invoked. The shell does not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used.
OPTARG. Optind refers to a variable that contains the argument of the option (if any, see the optstring option)

At the end of the process, OPTIND is set to the index of the first non-option argument, and name is set to ?.

Return value

When the end of options is encountered, getopts exits with a return value greater than zero.

getopts returns:

true if an option, specified or unspecified, is found.
false if the end of options is encountered or an error occurs.

Error reporting

If the first character of optstring is a colon, silent error reporting is used.

Silent Error Reporting

If the variable OPTERR is set to:

0: no error messages will be displayed, even if the first character of optstring is not a colon.
otherwise messages are printed when invalid options or missing option arguments are encountered.

If a required argument is not found:

name gets a colon (:)
OPTARG is set to the option character found.

No Silent Error Reporting