#!/usr/bin/perl -w
use 5.011;
use Data::Dumper;

open my $inFH, q{<}, \ <<__EOD__ or die $!;
abcdef
abcdefg
abcde
 bcdefgh
 bcd    
__EOD__

chomp( my @lines = <$inFH> );
close $inFH or die $!;

my $width  = 6;
my $height = 4;

my $raRect = makeRect( \ @lines, $width, $height );

print Data::Dumper->Dumpxs( [ $raRect ], [ qw{ raRect } ] );

sub makeRect
{
    my( $raLines, $width, $height ) = @_;
    my @rect;
    push @rect, pack qq{A$width}, shift @{ $raLines } for 1 .. $height;
    return \ @rect;
}