Reference: defined
Author: Ellen Siever, Stephen Spainhour & Nathan Patwardhan
Date: 1999-07-02T01:34:32Z

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| Chapter 5 Function Reference |

## defined

    defined expr

Returns a Boolean value saying whether the scalar value resulting from expr has a real value or not. If no argument is given, `defined` checks `$_`.

A scalar that contains no valid string, numeric, or reference value is known as the undefined value, or `undef` for short. Many operations return the undefined value under exceptional conditions, such as end of file, uninitialized variable, system error, and such. This function allows you to distinguish between an undefined null string and a defined null string when you're using operators that might return a real null string.

You can use `defined` to see if a subroutine exists, that is, if the subroutine definition has been successfully parsed. However, using `defined` on an array or a hash is not guaranteed to produce intuitive results, and should be avoided.

Reference: dbmopen |  | Reference: delete