replace.pl

use strict;
use warnings;
use utf8;

use File::Find;
use IO::File;

File::Find::find({ wanted => \&wanted, no_chdir => 1}, '.');

sub wanted {
    my $path = $File::Find::name;

    if (-f $path && $path =~ m{\.html\z}xms) {
        printf STDERR "[start] %s\n", $path;
        my $text = slurp($path);
        $text = replace_ssi_tag($text);
        write_file($path, $text);
        printf STDERR "[end] %s\n", $path;
    }
}

sub replace_ssi_tag {
    my ($text) = @_;

    $text =~ s{\#INCLUDE \s+ VIRTUAL}{# include virtual}xms;
    return $text;
}

sub slurp {
    my ($path) = @_;

    my $fh = IO::File->new($path, 'r') or die "Can't read $path: $!";

    local $/ unless wantarray;
    return <$fh>;
}

sub write_file {
    my ($path, $text) = @_;

    my $fh = IO::File->new($path, 'w') or die "Can't read $path: $!";
    $fh->print($text);
    $fh->close();
}