Programming Perl, 4th Edition

Handle References

References to filehandles or directory handles can be created by referencing the typeglob of the same name:

splutter(\*STDOUT);

sub splutter {
    my $fh = shift;
    say $fh "her um well a hmmm";
}

$rec = get_rec(\*STDIN);
sub get_rec {
    my $fh = shift;
    return scalar <$fh>;
}

If you’re passing around filehandles, you can also use the bare typeglob to do so: in the example above, you could have used *STDOUT or *STDIN instead of \*STDOUT and \*STDIN.

Although you can usually use typeglobs and references to typeglobs interchangeably, there are a few places where you can’t. Simple typeglobs can’t be blessed into objectdom, and typeglob references can’t be passed back out of the scope of a localized typeglob.

When generating new filehandles, older code would often do something like this to open a list of files:

for $file (@names) {
    local *FH;
    open(*FH, $file) || next;
    $handle{$file} = *FH;
}

That still works, but it’s often preferable to let an undefined variable autovivify an anonymous typeglob:

for $file (@names) {
    my $fh;
    open($fh, $file) || next;
    $handle{$file} = $fh;
}

Anytime you have a variable that contains a filehandle instead of a bareword handle, you have an indirect filehandle. It doesn’t matter whether you use strings, typeglobs, references to typeglobs, or one of the more exotic I/O objects. You just use a scalar that—one way or another—gets interpreted as a filehandle. For most purposes, you can use either a typeglob or a typeglob reference almost indiscriminately. As ...