To test if something is a filehandle, use the fileno() function, like this: 
if (defined(fileno($fh))) {
    print "Filehandle!\n";
} else {
    print "Not a filehandle\n";
}

[download]
fileno() works as you'd expect on both bare filehandles (eg, STDERR) and on references (eg, those returns from CGI::param and CGI::upload).

Trap for the unwary: Zero is a perfectly legal fileno, which is usually bound to STDIN. Hence you should always check to make sure that fileno returns a defined value, not just a true one. Otherwise you can get caught out if you're testing STDIN for filehandle-ness, or if your STDIN has been closed and something else has taken fileno 0 as its own.

Cheers,
Paul

In reply to Re: How to verify a file handle? by pjf
in thread How to verify a file handle? by Anonymous Monk

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