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Perl 5 version 20.2 documentation
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  • ref EXPR

  • ref

    Returns a non-empty string if EXPR is a reference, the empty string otherwise. If EXPR is not specified, $_ will be used. The value returned depends on the type of thing the reference is a reference to.

    Builtin types include:

    1. SCALAR
    2. ARRAY
    3. HASH
    4. CODE
    5. REF
    6. GLOB
    7. LVALUE
    8. FORMAT
    9. IO
    10. VSTRING
    11. Regexp

    You can think of ref as a typeof operator.

    1. if (ref($r) eq "HASH") {
    2. print "r is a reference to a hash.\n";
    3. }
    4. unless (ref($r)) {
    5. print "r is not a reference at all.\n";
    6. }

    The return value LVALUE indicates a reference to an lvalue that is not a variable. You get this from taking the reference of function calls like pos() or substr(). VSTRING is returned if the reference points to a version string.

    The result Regexp indicates that the argument is a regular expression resulting from qr//.

    If the referenced object has been blessed into a package, then that package name is returned instead. But don't use that, as it's now considered "bad practice". For one reason, an object could be using a class called Regexp or IO , or even HASH . Also, ref doesn't take into account subclasses, like isa does.

    Instead, use blessed (in the Scalar::Util module) for boolean checks, isa for specific class checks and reftype (also from Scalar::Util) for type checks. (See perlobj for details and a blessed/isa example.)

    See also perlref.