FAQ 4.40 What is the difference between $array[1] and @array[1]?

Discussion in 'Perl Misc' started by PerlFAQ Server, Apr 16, 2011.

  1. This is an excerpt from the latest version perlfaq4.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 .

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

    4.40: What is the difference between $array[1] and @array[1]?

    (contributed by brian d foy)

    The difference is the sigil, that special character in front of the
    array name. The "$" sigil means "exactly one item", while the "@" sigil
    means "zero or more items". The "$" gets you a single scalar, while the
    "@" gets you a list.

    The confusion arises because people incorrectly assume that the sigil
    denotes the variable type.

    The $array[1] is a single-element access to the array. It's going to
    return the item in index 1 (or undef if there is no item there). If you
    intend to get exactly one element from the array, this is the form you
    should use.

    The @array[1] is an array slice, although it has only one index. You can
    pull out multiple elements simultaneously by specifying additional
    indices as a list, like @array[1,4,3,0].

    Using a slice on the lefthand side of the assignment supplies list
    context to the righthand side. This can lead to unexpected results. For
    instance, if you want to read a single line from a filehandle, assigning
    to a scalar value is fine:

    $array[1] = <STDIN>;

    However, in list context, the line input operator returns all of the
    lines as a list. The first line goes into @array[1] and the rest of the
    lines mysteriously disappear:

    @array[1] = <STDIN>; # most likely not what you want

    Either the "use warnings" pragma or the -w flag will warn you when you
    use an array slice with a single index.



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    PerlFAQ Server, Apr 16, 2011
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