#print $channel "$cmd\n";
    #while (<$channel>) {
    print {${$channel}} "$cmd\n";
    while (<${$channel}>) {

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

sub print_to_fh
{
  my ( $ref_to_fh ) = @_;
  #$ref_to_fh is _not_ a filehandle. It's a scalar, that's a reference. 
  print $ref_to_fh "Some text\n";
}

open ( my $filehandle, ">", "testfile.txt" );
&print_to_fh ( \$filehandle );
close ( $filehandle ); 

##</code><code>##

sub print_to_fh
{
  my ( $ref_to_fh ) = @_;
  #$ref_to_fh is _not_ a filehandle. It's a scalar, that's a reference.  
  my $filehandle = $$ref_to_fh;
  #Filehandle has dereferenced $ref_to_fh, so we can print to it now:
  print $filehandle "Some more text\n";
}

open ( my $filehandle, ">", "testfile.txt" );
&print_to_fh ( \$filehandle );
close ( $filehandle ); 

##</code><code>##

  print {$$ref_to_fh} "Even more stuff\n";