use strict;
use warnings;

my $data;

#write to filehandle 
open WH, ">", "test$$.txt" or die $!;
_write(*WH, "This is a test\n");
close WH;

#read from filehandle into $data
open RH, "test$$.txt" or die $!;
_read(*RH, \$data);
close RH;

print $data;

sub _write {
    my $fh = shift;
    my $data  = shift;
    print $fh $data or die $!
}

sub _read {
    my $fh = shift;
    my $data  = shift;
    $$data .= $_ while <$fh>
}