Perl, GPG, and --passphrase-fd

[christopher.a.feathers@accenture.com]

I saw a few postings in previous months that posed the question:

"How do I invoke decryption with a passphrase and avoid getting prompted
for a passphrase?"

Browsing through the gpg.man page I found an option of:

       --passphrase-fd n
                 Read  the  passphrase from file descriptor n. If
                 you use 0 for n, the  passphrase  will  be  read
                 from  stdin.     This  can  only be used if only
                 one passphrase  is  supplied.   Don't  use  this
                 option if you can avoid it.

That is great! - but I cannot seem to figure how to get at the file
descriptor that Perl is looking to use.  Has anyone used this option?

Thanks a bunch.... this is driving me crazy.

-Chris