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Typeglobs and Filehandles

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Typeglobs and Filehandles

Perl uses an internal type called a typeglob to hold an entire symbol table entry. The type prefix of a typeglob is a *, because it represents all types. This used to be the preferred way to pass arrays and hashes by reference into a function, but now that we have real references, this is seldom needed. It also used to be the preferred way to pass filehandles into a function, but now that we have the *foo{THING} notation it isn't often needed for that, either. It is still needed to pass new filehandles into functions (*HANDLE{IO} only works if HANDLE has already been used).

If you need to use a typeglob to save away a filehandle, do it this way:

    $fh = *STDOUT;

or perhaps as a real reference, like this:

    $fh = \*STDOUT;

This is also a way to create a local filehandle. For example:

    sub newopen {
        my $path = shift;
        local *FH;  # not my!
        open (FH, $path) || return undef;
        return *FH;
    $fh = newopen('/etc/passwd');

Another way to create local filehandles is with IO::Handle and its ilk, see the bottom of open().

See the perlref manpage, the perlsub manpage, and Symbol Tables for more discussion on typeglobs.

Source: Perl data types
Copyright: Larry Wall, et al.

Previous: List value constructors

(Corrections, notes, and links courtesy of RocketAware.com)

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