$array1[$k] =~ s/^\s+//;
$array1[$k] =~ s/\s+$//;
$array2[$l] =~ s/^\s+//;
$array2[$l] =~ s/\s+$//;

##</code><code>##

# modify value in place
sub trim {
    $_[0] =~ s/^\s+//;
    $_[0] =~ s/\s+$//;
}

trim($array1[$k]);
trim($array2[$l]);

# --- or ---

# return the trimmed value
sub trim {
    my $s = shift;
    $s =~ s/^\s+//;
    $s =~ s/\s+$//;
    return $s;
}

$array1[$k] = trim($array1[$k]);
$array2[$l] = trim($array2[$l]);