if ($read) {
  if ($more) {
    # do something
  }
}

##</code><code>##

#!/usr/bin/perl -w

#or
use warnings;

##</code><code>##

foreach $line (@File_pre_format) {
  $file_pre_format .= $line;
}
# better:
$file_pre_format = join '', @File_pre_format;

$file_pre_format =~ s/\n//g;
$file_pre_format =~ s/\t//g;
# better:
$file_pre_format =~ s/\n|\t//g;
# or in this simple case even better:
$file_pre_format =~ tr/\n\t//d;