FAQ 7.20 Why doesn't "my($foo) = <FILE>;" work right?

Discussion in 'Perl Misc' started by PerlFAQ Server, Feb 28, 2011.

  1. This is an excerpt from the latest version perlfaq7.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    7.20: Why doesn't "my($foo) = <FILE>;" work right?

    "my()" and "local()" give list context to the right hand side of "=".
    The <FH> read operation, like so many of Perl's functions and operators,
    can tell which context it was called in and behaves appropriately. In
    general, the scalar() function can help. This function does nothing to
    the data itself (contrary to popular myth) but rather tells its argument
    to behave in whatever its scalar fashion is. If that function doesn't
    have a defined scalar behavior, this of course doesn't help you (such as
    with sort()).

    To enforce scalar context in this particular case, however, you need
    merely omit the parentheses:

    local($foo) = <FILE>; # WRONG
    local($foo) = scalar(<FILE>); # ok
    local $foo = <FILE>; # right

    You should probably be using lexical variables anyway, although the
    issue is the same here:

    my($foo) = <FILE>; # WRONG
    my $foo = <FILE>; # right



    --------------------------------------------------------------------

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    so please include as much information as possible and relevant in any
    corrections. The perlfaq-workers also don't have access to every
    operating system or platform, so please include relevant details for
    corrections to examples that do not work on particular platforms.
    Working code is greatly appreciated.

    If you'd like to help maintain the perlfaq, see the details in
    perlfaq.pod.
    PerlFAQ Server, Feb 28, 2011
    #1
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