Thnx for your help, this is what I was looking for :

#!/usr/bin/perl
use warnings;
use strict;

my @row;
my @f_map = ('f1', 'f2');
my $f = "format = \n"
        . ('^' . '<' x 15 . '|') x scalar(@f_map) . "\n"
        . '@row' . "\n"
        . ('^' . '<' x 15 . '|') x scalar(@f_map) . "~~\n"
        . '@row' . "\n"
        . ".\n";
eval($f);

# 
@row = ('blah1' x 10, 'blah2' x 10);
write;
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output :

blah1blah1blah1b|blah2blah2blah2b|
lah1blah1blah1bl|lah2blah2blah2bl|
ah1blah1blah1bla|ah2blah2blah2bla|
h1              |h2              |
[download]