Bash

📦 Bash Libraries & getopts (Option Parsing)

Creating modular, maintainable Bash scripts is crucial for large projects. This includes separating code into reusable files and parsing CLI flags using getopts.

📁 1. Creating a Library File (lib/log.sh)

Modular scripts allow you to split reusable functions into external .sh files.

lib/log.sh

#!/bin/bash

log_info() {
  echo "[INFO] $1"
}

log_error() {
  echo "[ERROR] $1" >&2
}

Main Script:

#!/bin/bash
source lib/log.sh

log_info "Script started"
log_error "Something went wrong"

🧩 2. Using source to Import Files

source ./utils.sh

or simply:

. ./utils.sh

This runs the file in the current shell, allowing access to its functions and variables.

⚙️ 3. Parsing Options with getopts

getopts is a Bash built-in used to handle command-line flags like -f, -v, -h.

Syntax:

while getopts ":f:v:h" opt; do
  case $opt in
    f) file=$OPTARG ;;
    v) value=$OPTARG ;;
    h) echo "Help message"; exit 0 ;;
    \?) echo "Invalid option: -$OPTARG" >&2 ;;
  esac
done

Example:

#!/bin/bash

while getopts ":n:a:" opt; do
  case $opt in
    n) name="$OPTARG" ;;
    a) age="$OPTARG" ;;
    \?) echo "Invalid option: -$OPTARG" ;;
  esac
done

echo "Name: $name"
echo "Age: $age"

Run it like:

./script.sh -n Kashif -a 24

🧠 Tips for getopts

Symbol Meaning
: after a letter Option requires an argument
\? Catch invalid options
: (before string) Suppress error messages (silent mode)

🔄 Optional: Long Options (with getopt)

Bash getopts does not support long options like --help directly. You can use GNU getopt for advanced parsing:

getopt -o h --long help -- "$@"

📌 Best Practices

Practice Benefit
Use source for reusable code Cleaner scripts
Group related functions Easier maintenance
Always validate arguments Prevent errors
Provide a -h or --help flag Friendly UX

📚 References

📁 File: advance/libraries-getopts.md
Author: Kashif Alam

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