package TestModul;

sub do_open {
   local $_;
   open FH,'<','./test.txt' or die $!;
   while (<FH>) {
      print;
   }
   close FH;
}

1;

use TestModul;

open FH,'<','./test.txt' or die $!;

while (<FH>) {
   TestModul->do_open;
   print;
}

close FH;

open( FH, $file1 ) or die $!;
my $filter = &GetFilter($filterFile);
my @lines = <FH>;
close( FH );

sub GetFilter {
  my ($file) = @_;
  open( FH, $file) or die $!; # schliesst das aeussere FH
  my $filter = <FH>;
  close(FH);
  return $filter;
}

#!/usr/bin/perl

use strict;
use warnings;

open(FH,"test.txt") or die $!;
while(<FH>){
  methode();
}
close FH;

sub methode{
  open(FH,"test2.txt") or die $!;
  close FH;
}

C:\Perl\community\studium>fileh.pl
readline() on closed filehandle FH at C:\Perl\community\studium\fileh.pl line 8.

my $content = do {
  local $/; # slurp mode
  open (my $FH, "<", $file) or die "Error in reading file '$file': $!\n";
  <FH>;
}; # do

close $fh or die $!