bin/grepchunk: process diff -u output and select/drop (-v) chunks like grep would

... if each chunk was a single line.

bin/grepchunk

@@ -0,0 +1,64 @@
+#!/usr/bin/perl
+
+
+sub usage
+{
+	print STDERR "usage: $0 [-v] pattern [file ...]\n";
+	exit(1);
+}
+
+
+if ($ARGV[0] eq "-v") {
+	$invert = 1;
+	shift @ARGV;
+}
+&usage if $ARGV[0] =~ /^-/;
+
+$pattern = shift @ARGV;
+&usage unless defined $pattern;
+
+
+sub flush
+{
+	my $mismatch = !($chunk =~ /$pattern/m);
+
+	if ($mismatch == $invert) {
+		print $head;
+		print $chunk;
+	}
+	undef $head;
+	undef $chunk;
+}
+
+
+$HEAD = 0;
+$CHUNK = 1;
+$TAIL = 2;
+
+
+$state = $HEAD;
+while (<>) {
+	$state = $HEAD if /^diff /;
+	if (/^@@ -\d+,(\d+) \+\d+,(\d+)/) {
+		$state = $CHUNK;
+		($in, $out) = ($1, $2);
+		$chunk = $_;
+		next;
+	}
+	if ($state == $HEAD) {
+		$head .= $_;
+		next;
+	}
+	next if $state == $TAIL;
+	$in-- if /^-/;
+	$out-- if /^\+/;
+	($in--, $out--) if /^\s/;
+	die "in $in out $out" if $in < 0 || $out < 0;
+	if ($in+$out == 0) {
+		$state = $TAIL;
+		&flush;
+	} else {
+		$chunk .= $_;
+	}
+}
+&flush;