replace-literal

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

# Display usage information
usage() {
	cat <<EOF
Usage: $(basename "$0") -f|--from <string> -t|--to <string> [<file>...]

Replace literal string occurrences in files or stdin (not regex).

Options:
    -f, --from <string>    String to search for (literal)
    -t, --to <string>      String to replace with (literal)
    -h, --help             Display this help message

Arguments:
    <file>...              Files to process (optional, reads from stdin if omitted)

Examples:
    $(basename "$0") -f 'foo' -t 'bar' file1.txt file2.txt
    echo 'foo bar' | $(basename "$0") -f 'foo' -t 'bar'
EOF
	exit "${1:-0}"
}

# Initialize variables
from_string=""
to_string=""
files=()

# Parse command line arguments
while [[ $# -gt 0 ]]; do
	case "$1" in
	-f | --from)
		if [[ -z "${2:-}" ]]; then
			echo "Error: --from requires an argument" >&2
			usage 1
		fi
		from_string="$2"
		shift 2
		;;
	-t | --to)
		if [[ -z "${2:-}" ]]; then
			echo "Error: --to requires an argument" >&2
			usage 1
		fi
		to_string="$2"
		shift 2
		;;
	-h | --help)
		usage 0
		;;
	-*)
		echo "Error: Unknown option: $1" >&2
		usage 1
		;;
	*)
		files+=("$1")
		shift
		;;
	esac
done

# Validate required arguments
if [[ -z "$from_string" ]]; then
	echo "Error: --from is required" >&2
	usage 1
fi

if [[ -z "$to_string" ]]; then
	echo "Error: --to is required" >&2
	usage 1
fi

# Find a delimiter character that doesn't appear in from_string or to_string
# Try common delimiters in order of preference
delimiter=""
for char in '/' '#' '@' '|' '~' '%' ',' ':' ';' '!' '^' '-' '_' '='; do
	if [[ "$from_string" != *"$char"* && "$to_string" != *"$char"* ]]; then
		delimiter="$char"
		break
	fi
done

if [[ -z "$delimiter" ]]; then
	echo "Error: Cannot find a safe delimiter character for the given strings" >&2
	exit 1
fi

# Process stdin if no files specified
if [[ ${#files[@]} -eq 0 ]]; then
	# Use perl with \Q...\E for literal string replacement
	# -pe: print each line after processing
	# \Q...\E: quote (disable) pattern metacharacters for literal matching
	perl -pe "s${delimiter}\Q$from_string\E${delimiter}$to_string${delimiter}g"
	exit 0
fi

# Process each file
for file in "${files[@]}"; do
	if [[ ! -f "$file" ]]; then
		echo "Error: File not found: $file" >&2
		exit 1
	fi

	if [[ ! -r "$file" ]]; then
		echo "Error: Cannot read file: $file" >&2
		exit 1
	fi

	if [[ ! -w "$file" ]]; then
		echo "Error: Cannot write to file: $file" >&2
		exit 1
	fi

	# Use perl with \Q...\E for literal string replacement
	# -i: edit in place
	# -pe: print each line after processing
	# \Q...\E: quote (disable) pattern metacharacters for literal matching
	perl -i -pe "s${delimiter}\Q$from_string\E${delimiter}$to_string${delimiter}g" "$file"
done