Escape POSIX (grep, sed, ex) regular expression patterns and replacements

escape-strings.sh

#!/bin/sh

# Functions to escape strings for use in utilities like grep, sed and ex

# Examples
# grep "$(bre "$foo")" file
# sed "s/$(ptrn "$foo")/$(repl "$bar")/g" file
# echo "s/$(exptrn "$foo")/$(exrepl "$bar")/g | %p | q" | ex file

bre() {
	# Escape string for use in POSIX BRE
	# Chars: [ \ . * $ ^
	printf '%s\n' "$1" | sed 's/[[\.*]/\\&/g; s/$$/\\&/; s/^^/\\&/'
}

ptrn() {
	# Escape string for use in slash-delimited BRE pattern
	# Chars: [ \ . * / $ ^
	printf '%s\n' "$1" | sed 's/[[\.*/]/\\&/g; s/$$/\\&/; s/^^/\\&/'
}

repl() {
	# Escape string for use in slash-delimited replacement
	# Chars: \ & /
	printf '%s\n' "$1" | sed 's/[\&/]/\\&/g'
}

exptrn() {
	# Escape string for use in ex pattern
	# Chars: [ \ . * / ~ $ ^
	printf '%s\n' "$1" | sed 's/[[\.*/~]/\\&/g; s/$$/\\&/; s/^^/\\&/'
}

exrepl() {
	# Escape string for use in ex replacement
	# Chars: \ & / ~
	printf '%s\n' "$1" | sed 's/[\&/~]/\\&/g'
}