NAME

Raku port of Perl's fileno() built-in

SYNOPSIS

use P5fileno;

say fileno $*IN;    # 0
say fileno $*OUT;   # 1
say fileno $*ERR;   # 2
say fileno $foo;    # something like 16

DESCRIPTION

This module tries to mimic the behaviour of Perl's fileno built-in as closely as possible in the Raku Programming Language.

ORIGINAL PERL 5 DOCUMENTATION

fileno FILEHANDLE
        Returns the file descriptor for a filehandle, or undefined if the
        filehandle is not open. If there is no real file descriptor at the
        OS level, as can happen with filehandles connected to memory
        objects via "open" with a reference for the third argument, -1 is
        returned.

        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) != -1 && fileno(THIS) == fileno(THAT)) {
                print "THIS and THAT are dups\n";
            } elsif (fileno(THIS) != -1 && fileno(THAT) != -1) {
                print "THIS and THAT have different " .
                    "underlying file descriptors\n";
            } else {
                print "At least one of THIS and THAT does " .
                    "not have a real file descriptor\n";
            }

IDIOMATIC PERL 6 WAY

The file descriptor of a file handle is exposed with the native-descriptor method on IO::Handle:

say $*OUT.native-descriptor;   # 1

PORTING CAVEATS

When calling with an unopened IO::Handle, this version will return Nil. That's the closest thing there is to undef in Raku.

AUTHOR

Elizabeth Mattijsen [email protected]

Source can be located at: https://github.com/lizmat/P5fileno . Comments and Pull Requests are welcome.

COPYRIGHT AND LICENSE

Copyright 2018, 2019, 2020, 2021 Elizabeth Mattijsen

Re-imagined from Perl as part of the CPAN Butterfly Plan.

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.