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undef EXPR

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undef EXPR

undef

Undefines the value of EXPR, which must be an lvalue. Use only on a scalar value, an entire array, an entire hash, or a subroutine name (using ``&''). (Using undef() will probably not do what you expect on most predefined variables or DBM list values, so don't do that.) Always returns the undefined value. You can omit the EXPR, in which case nothing is undefined, but you still get an undefined value that you could, for instance, return from a subroutine, assign to a variable or pass as a parameter. Examples:

    undef $foo;
    undef $bar{'blurfl'};             # Compare to: delete $bar{'blurfl'};
    undef @ary;
    undef %hash;
    undef &mysub;
    return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
    select undef, undef, undef, 0.25;
    ($a, $b, undef, $c) = &foo;       # Ignore third value returned

Source: Perl builtin functions
Copyright: Larry Wall, et al.

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