Linux getopts Guide

Linux getopts Guide

Complete beginner-friendly guide to getopts on Linux, covering Arch Linux, CachyOS, and other distributions including built-in option parsing, shell option handling, and script argument parsing.

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Table of Contents

1. getopts Basics
2. Option Parsing
3. Options with Arguments
4. Error Handling
5. Troubleshooting

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getopts Basics

Parse Options

Basic usage:

#!/bin/bash
while getopts "hv" opt; do
    case $opt in
        h)
            echo "Help"
            ;;
        v)
            VERBOSE=1
            ;;
    esac
done

Option String

Option format:

# Option string: "hv"
# h = help flag
# v = verbose flag

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Option Parsing

Simple Options

Basic flags:

#!/bin/bash
while getopts "hv" opt; do
    case $opt in
        h) echo "Help message" ;;
        v) VERBOSE=1 ;;
        \?) echo "Invalid option" ;;
    esac
done

Multiple Options

Multiple flags:

# Multiple options
while getopts "abc" opt; do
    case $opt in
        a) OPTION_A=1 ;;
        b) OPTION_B=1 ;;
        c) OPTION_C=1 ;;
    esac
done

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Options with Arguments

Required Arguments

Option with value:

# Option with argument
while getopts "f:" opt; do
    case $opt in
        f)
            FILE=$OPTARG
            ;;
    esac
done

# Usage: script.sh -f filename.txt

Optional Arguments

Optional value:

# Optional argument (GNU extension)
while getopts "f::" opt; do
    case $opt in
        f)
            FILE=${OPTARG:-default.txt}
            ;;
    esac
done

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Error Handling

Invalid Options

Handle errors:

#!/bin/bash
while getopts "hv" opt; do
    case $opt in
        h) echo "Help" ;;
        v) VERBOSE=1 ;;
        \?)
            echo "Invalid option: -$OPTARG" >&2
            exit 1
            ;;
        :)
            echo "Option -$OPTARG requires argument" >&2
            exit 1
            ;;
    esac
done

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Troubleshooting

getopts Not Found

Check installation:

# getopts is built-in shell command
# Always available in bash

# Check bash
which bash

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Summary

This guide covered getopts usage, built-in option parsing, and script argument handling for Arch Linux, CachyOS, and other distributions.

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Next Steps

• getopt Guide - External option parser
• Bash Scripting Guide - Scripting basics
• getopts Documentation: man bash (built-in)

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This guide covers Arch Linux, CachyOS, and other Linux distributions. For distribution-specific details, refer to your distribution's documentation.