Actually, as fate would have it, it doesn't segfault for me :). It does give a warning during the run, however; that may hint in the right direction.

This is perl, v5.8.9 built for amd64-freebsd

Ah. It segfaults for me on 5.8.8. And yes, the warning likely does give a useful hint.

I'm having a hard time with it. I've narrowed down, I think, the crash to this regex in Template::Parser:

    while ($text =~ s/
           ^(.*?)               # $1 - start of line up to directive
           (?:
            $start          # start of tag
            (.*?)           # $2 - tag contents
            $end            # end of tag
            )
           //sx) {
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#!/usr/bin/perl

use strict;
use warnings;
use Template;
#use Template::Parser;

my $template = Template->new({});

my $text = "[% SET content='" . ("stuff "x20_000) . "' %]";

my $start = qr/\Q[%/;
my $end   = qr/\Q%]/;
while ($text =~ s/
       ^(.*?)               # $1 - start of line up to directive
       (?:
       $start          # start of tag
       (.*?)           # $2 - tag contents
       $end            # end of tag
       )
       //sx) {
    #print "1=$1\n2=$2\n";
}

pos($text) = 0;

$template->process(\$text, {});

print "Processed\n";
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(Perl 5.8.8 here)

You have the right idea and module, but the wrong regular expression.

I started by creating a local copy of Template that I could add debugging statements to. Using a binary search I found the last function call within process it executed, then went to that function and found where it died there, and before long found the actual place where it dies.