# gosub(regexp, replacement [, target])
# Aka global original sub
# Behaves like gsub, however doesn't try regexp on previoud replacements
# and returns the result string, rather than doing it inplace.
function gosub(regexp, replacement, target) {
	if (!length(target)) {
		target = $0;
	}

	result = "";
	matched = "";
	while (match(target, regexp)) {
		result = result substr(target, 1, RSTART - 1);
		matched = substr(target, RSTART, RLENGTH);
		target = substr(target, RSTART + RLENGTH);

		sub(regexp, replacement, matched);
		result = result matched;
	}

	return result target;
}

# gesub(regexp, exregexp, replacement [, target])
# Aka global excluding sub
# Behaves like gsub, however substitutes only where exregexp doesn't match
# and returns the result string, rather than doing it inplace.
function gesub(regexp, exregexp, replacement, target) {
	if (!length(target)) {
		target = $0;
	}

	result = "";
	while (match(target, exregexp)) {
		beg = substr(target, 1, RSTART - 1);
		exclude = substr(target, RSTART, RLENGTH);
		target = substr(target, RSTART + RLENGTH);
		gsub(regexp, replacement, beg);
		result = result beg exclude;
	}

	gsub(regexp, replacement, target);

	return result target;
}

# glsub(lbregexp, regexp, largexp, replacement [, target])
# Aka global sub with non-capturing look-around (lookbehind and lookahead)
# Behaves kind of like gsub, however substitution of regexp with replacement
# only happens, when regexp is preceded by lbregexp and succeeded by laregexp.
# Only regexp get's replaced, the matches of lbregexp and laregexp are left
# as-is. Overlapping of the lookahead and lookbehind substrings is supported,
# but any sort of overlapping which includes regexp isn't.
# This function is quite slow, try to use as little as possible.
# Returns the result string, rather than doing it inplace.
function glsub(lbregexp, regexp, laregexp, replacement, target) {
	if (!length(target)) {
		target = $0;
	}

	result = ""
	while (match(target, lbregexp regexp)) {
		result = result substr(target, 1, RSTART - 1);
		matched = substr(target, RSTART, RLENGTH);
		target = substr(target, RSTART + RLENGTH);
		
		match(target, laregexp);
		if (RSTART == 1) {
			match(matched, regexp);
			result = result substr(matched, 1, RSTART - 1);
			matched = substr(matched, RSTART);
			sub(/.*/, replacement, matched);
		}
		result = result matched;
	}

	return result target;
}

# gbsub(lbrace, rbrace, replacement [, target ])
# Aka global brace sub
# Properly substitutes recursive braced expressions, i.e.
# for "((1+2) * (3/(4-9)))", substitution is done first
# on "(1+2)", then on "(4-9)", afterwards on "(3/SOMETHING)"
# (where "(4-9)" turns into "SOMETHING" after substitution),
# and finally, the whole equation (with it's inner stuff
# substituted) is substituted.
# This is useful when one of the braces can exist as-is, but
# can also be paired with a special (opening/closing) brace.
# For example, in bash parameter expansion is specified with
# "${...}", however "}" can also be the closing brace of a function.
function gbsub(lbrace, rbrace, replacement, target) {
	if (!length(target)) {
		target = $0;
	}
	
	result = substr(target, 1, match(target, lbrace) - 1);
	depth = 1;
	LLN = 0;
	while (!(LLN == -1 && depth == 1)) {
		match(target, lbrace); LST = RSTART; LLN = RLENGTH;
		match(target, rbrace);

		# rbrace, pop stack
		if (depth > 1 && (LST == 0 || LST > RSTART)) {
			depth--;
			level[depth] = level[depth] substr(target, 1, RSTART + RLENGTH - 1);
			sub(/.*/, replacement, level[depth]);
			if (depth > 1) {
				level[depth - 1] = level[depth - 1] level[depth];
			}
			else {
				result = result level[1];
				level[1] = "";
			}
			target = substr(target, RSTART + RLENGTH);
		}
		# lbrace, push stack
		else if (LST > 0 && LST < RSTART) {
			if (depth > 1) prev = depth - 1;
			else prev = depth;

			level[prev] = level[prev] substr(target, 1, LST - 1);
			level[depth++] = substr(target, LST, LLN);
			target = substr(target, LST + LLN);
		}
	}

	return result target;
}