ShellPatternsToRegex.bash

#!/bin/bash
# shellcheck disable=SC1003
set -eEuo pipefail

# Converts a list of wildcard patterns, as defined by glob(7) and used
# by e.g. GNU find for the -path switch, to a single regular
# expression.
function ShellPatternsToRegex() {
 	local patterns=("$@")

	local regexps=()
	local pattern
	for pattern in "${patterns[@]}"
	do
		local regexp='^'
		while [[ "$pattern" =~ ^([^][*?$\(\)*+.\\^{|]*)([][*?$\(\)*+.\\^{|}])(.*)$ ]] # split by glob special character
		do
			regexp=$regexp${BASH_REMATCH[1]}
			pattern=${BASH_REMATCH[3]}
			case "${BASH_REMATCH[2]}" in
				'[')
					if [[ "$pattern" =~ ^(!?)(\]?[^]]*\])(.*)$ ]]
					then
						regexp=$regexp'['
						if [[ -n "${BASH_REMATCH[1]}" ]]
						then
							regexp=$regexp'^'
						fi
						regexp=$regexp${BASH_REMATCH[2]}
						pattern=${BASH_REMATCH[3]}
					else # '[' without matching ']'
						regexp=$regexp'\['
					fi
					;;
				'*')
					regexp=$regexp'.*'
					;;
				'?')
					regexp=$regexp'.'
					;;
				'^'|']')
					regexp=$regexp'\'"${BASH_REMATCH[2]}"
					;;
				*)
					regexp=$regexp'['"${BASH_REMATCH[2]}"']'
					;;
			esac
		done
		regexp=$regexp$pattern'$'
		regexps+=("$regexp")
	done
	
	( IFS='|' ; echo "${regexps[*]}" )
}

: Test
ShellPatternsToRegex '*'
ShellPatternsToRegex 'a?c'
ShellPatternsToRegex 'a[b'
ShellPatternsToRegex 'a[b]c'
ShellPatternsToRegex 'a[!b]c'
ShellPatternsToRegex 'a[][]c'
ShellPatternsToRegex 'a[!][]c'
ShellPatternsToRegex 'a*' 'b*' 'c*'

ShellPatternsToRegex 'a.b'
ShellPatternsToRegex 'a(b)c'
ShellPatternsToRegex 'a^c'
ShellPatternsToRegex 'a.*c'