acme/bin/s2t

#!/usr/bin/env bash

awk -v n_spaces="$1" '

BEGIN {
	tab = "	"
	space = " "

	if (n_spaces < 1)
		n_spaces = 4
}

function spaces_to_tabs(line) {
	n_leading_spaces = 0
	for (i = 1; i <= length(line); i += 1) {
		if (substr(line, i, 1) != space)
			break
		n_leading_spaces += 1
	}

	if ( (0 < n_leading_spaces) && (n_leading_spaces < n_spaces) )
		n_tabs = 1
	else
		n_tabs = int(n_leading_spaces / n_spaces)

	tabs = ""
	while (n_tabs--)
		tabs = tabs tab

	return tabs substr(line, i)
}

{ print spaces_to_tabs($0) }

'