Parsing Command Line Arguments in Bash with `getopts`

#!/bin/bash

# --- Default values ---
NAME="World"
VERBOSE=0
OUTPUT_FILE=""

# --- Usage function ---
usage() {
    echo "Usage: $0 [-n <name>] [-v] [-o <output_file>]"
    echo "  -n <name>      Specify a name (default: World)"
    echo "  -v             Enable verbose mode"
    echo "  -o <output_file> Redirect output to a file"
    exit 1
}

# --- Parse options with getopts ---
# The colon after 'n' and 'o' indicates that these options require an argument.
# The initial colon suppresses default error messages.
while getopts ":n:vo:" opt; do
    case $opt in
        n)
            NAME="$OPTARG"
            ;;
        v)
            VERBOSE=1
            ;;
        o)
            OUTPUT_FILE="$OPTARG"
            ;;
        \?) # Invalid option
            echo "Invalid option: -$OPTARG" >&2
            usage
            ;;
        :) # Missing option argument
            echo "Option -$OPTARG requires an argument." >&2
            usage
            ;;
    esac
done

# Shift remaining arguments (non-options)
shift $((OPTIND-1))

# --- Apply output redirection if specified ---
if [ -n "$OUTPUT_FILE" ]; then
    exec > "$OUTPUT_FILE"
    if [ $? -ne 0 ]; then
        echo "Error: Could not redirect output to $OUTPUT_FILE." >&2
        exit 1
    fi
fi

# --- Main script logic ---
if [ "$VERBOSE" -eq 1 ]; then
    echo "Verbose mode enabled."
    echo "Hello $NAME!"
    echo "Script arguments processed."
    if [ -n "$OUTPUT_FILE" ]; then
        echo "Output redirected to: $OUTPUT_FILE"
    fi
    if [ "$#" -gt 0 ]; then
        echo "Remaining arguments: $*"
    fi
else
    echo "Hello $NAME!"
fi

echo "Script execution complete."