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P5fileno - Implement Perl's fileno() built-in
use P5fileno;
say fileno $*IN; # 0
say fileno $*OUT; # 1
say fileno $*ERR; # 2
say fileno $foo; # something like 16
This module tries to mimic the behaviour of the fileno function of Perl as closely as possible.
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";
}
The file descriptor of a file handle is exposed with the native-descriptor method on IO::Handle:
say $*OUT.native-descriptor; # 1
When calling with an unopened IO::Handle, this version will return Nil. That's the closest thing there is to undef in Raku.
Elizabeth Mattijsen [email protected]
Source can be located at: https://github.com/lizmat/P5fileno . Comments and Pull Requests are welcome.
Copyright 2018-2019 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.