What? No one's mentioned the swiss army chainsaw of of IO operations, IO::All ?

From the docs:

use IO::All;
my ($io, $contents);
$io = io 'file.txt';
$contents < $io;
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And if you want to write to the file, you've got that too:

# manipulate $contents to write it back out:
$contents > $io;
$some_extra_bit >> $io;
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---

Ignoring abominations like that module, there's also this trick:

  my $filename = 'thefile.txt';
  my $pid = open(FH, "-|");
  if (not defined $pid) {
    die "cannot fork: $!; bailing out";
  }
  if (! $pid) {
    exec('/bin/cat', $filename);
  }
  while (<FH>) { ... }
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Which trick is actually useful if you want to do more than open a file; e.g. if you want to run some external program that needs a special environment set up before you invoke it, like tying STDERR to STDOUT, or ensuring that STDIN is closed, or that the program is disassociated from the controlling terminal via a call to POSIX::setsid. (java processes that you want running in the background are sometimes picky about being completely disassociated from the controlling terminal)