use strict;
use warnings;
use Template;

my $tt = Template->new({ EVAL_PERL => 1 });

my $str = 'This is too verbose to be printed in its entirety';
     # 16 characters here ^

$tt->process(\*DATA, { string => $str }) || die $tt->error;

__DATA__
Original  string : [% string %]
Formatted string : [%- PERL -%]
    if ( length '[%- string -%]' > 16 ) {
        (my $truncated = '[%- string -%]') =~ s/^(.{0,16}\b).*$/$1.../s;
        print $truncated;
    }
    else {
        print '[% string %]';
    }
[%- END -%]

##</code><code>##

Original  string : This is too verbose to be printed in its entirety
Formatted string : This is too ...