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# fileno

Perl 5 version 10.1 documentation
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# fileno

Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage

- fileno FILEHANDLE

  Returns the file descriptor for a filehandle, or undefined if the filehandle is not open. This is mainly useful for constructing bitmaps for `select` and low-level POSIX tty-handling operations. If FILEHANDLE is an expression, the value is taken as an indirect filehandle, generally its name.

  You can use this to find out whether two handles refer to the same underlying descriptor:

          if (fileno(THIS) == fileno(THAT)) {	print "THIS and THAT are dups\n";    }

  (Filehandles connected to memory objects via new features of `open` may return undefined even though they are open.)

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