perl script.pl filename

#!/usr/bin/perl
my $s;
while (<>) {
  my ( $tag, $value ) = /^<(main|sub(\d+))>/
    or print STDERR "wrong tag on line $.\n" and next;
  $s = 0, next if $tag eq 'main';
  next if $value == ++$s;
  print STDERR "wrong sub expect $s got $value in line $.\n";
  $s = $value;
}
__OUTPUT__
wrong sub expect 2 got 3 in line 4
wrong sub expect 1 got 2 in line 6
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