Bash boilerplate code for parsing command-line args

copy_reinvented.sh

#/usr/bin/env bash

#set -euo pipefail

EXIT_SUCCESS=0
EXIT_FAILURE=1

IFS='' read -r -d '' USAGE <<HEREDOC

Copy-reinvented to showcase Bash heredoc usage and command-line arguments handling.

Use <<-HEREDOC to suppress leading tabs (but not spaces) in the output.
Use <<\HEREDOC or <<'HEREDOC' to disable parameter substitution within the heredoc body.
Test with a trailing backlash: \\
Test with more special characters: $EXIT_FAILURE < $EXIT_SUCCESS

Usage: $(basename "$0") [OPTIONS] <SOURCE> <DESTINATION>
Options:
    -f, --force-overwrite   When set to true (defaults to false), the file exists at DESTINATION will be overwritten
    -d, --dry-run           When set to true (defaults to false), the command to be executed will be printed to stdout
    -h, --help              Print this info
Example:
    $(basename "$0") --force-overwrite="true" --dry-run "source.txt" "destination.txt"

HEREDOC

# Parse options

for i in "$@"; do
    case $i in
        -f=*|--force-overwrite=*)
            # Get the value on the righ-hand side of the equal sign
            FORCE_OVERWRITE="${i#*=}"
            shift
            ;;
        -d|--dry-run)
            # Option of the flag style
            DRY_RUN="true"
            shift
            ;;
        -h|--help)
            echo "$USAGE"
            exit "$EXIT_SUCCESS"
            ;;
        -*)
            echo "Error: unknown option $i. Use '-h' for help."
            exit "$EXIT_FAILURE"
            ;;
    esac
done

# Set defaults using noop (:)

: ${FORCE_OVERWRITE="false"}
: ${DRY_RUN="false"}

# Get the positional parameters and do some validation at the same time

SOURCE=${1:?"Error: missing SOURCE. Use '-h' for help."}
DESTINATION=${2:?"Error: missing DESTINATION. Use '-h' for help."}

# Do the work

command="cp"

# Trim the parameter
if [[ "${FORCE_OVERWRITE// }" == "true" ]]; then
    command="$command -f"
fi

command="$command $SOURCE $DESTINATION"

if [[ "${DRY_RUN// }" == "true" ]]; then
    echo "$command"
else
    ${command}
fi