root/pretty.pl

#!/usr/bin/perl

use IO::Handle;
STDOUT->autoflush;
use strict;
my $indent = 0;
my $line;
while(defined ($line = <STDIN>)) {
  my $ix = 0;
  for my $ix (0 .. length($line)) {
    my $char = substr($line, $ix, 1);
    if (substr($line, $ix, 1) eq '<') {
      print '<';
      $indent += 2;
      print "\n";
      print " " x $indent;
    } elsif (substr($line, $ix, 1) eq '>') {
      $indent -= 2;
      print "\n";
      print " " x $indent;
      print '>';
    } else {
      print $char;
    }
  }
}