[English] Debian Almquist Shell (dash) getopts Usage: [parse command-line options]

Overview

The getopts command in the Debian Almquist Shell (dash) is used to parse command-line options in shell scripts. It simplifies the process of handling options and arguments, allowing scripts to accept flags and parameters in a standardized way.

Usage

The basic syntax of the getopts command is as follows:

getopts optstring variable

• optstring: A string that defines the valid options. Each option character can be followed by a colon (:) if it requires an argument.
• variable: The name of the variable that will store the option found.

Common Options

• -a: This option is not standard for getopts but is often used in scripts for custom handling.
• -b: Similar to -a, this is not a standard option but can be defined in the optstring.
• :: Indicates that the option requires an argument.

Common Examples

Example 1: Basic Option Parsing

This example shows how to parse a single option -a.

#!/bin/sh
while getopts "a" opt; do
  case $opt in
    a)
      echo "Option -a was triggered."
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      ;;
  esac
done

Example 2: Options with Arguments

In this example, we parse the -f option which requires an argument.

#!/bin/sh
while getopts "f:" opt; do
  case $opt in
    f)
      echo "File name: $OPTARG"
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      ;;
  esac
done

Example 3: Multiple Options

This example demonstrates how to handle multiple options, both with and without arguments.

#!/bin/sh
while getopts "a:b:c" opt; do
  case $opt in
    a)
      echo "Option -a with argument: $OPTARG"
      ;;
    b)
      echo "Option -b with argument: $OPTARG"
      ;;
    c)
      echo "Option -c was triggered."
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      ;;
  esac
done

Tips

• Always include a case for \? to handle invalid options gracefully.
• Use OPTIND to reset the index of the next option to be processed if you need to call getopts multiple times in your script.
• Keep your optstring clear and concise to avoid confusion when adding new options.