Name
defined
Synopsis
defined expr
Returns a Boolean value saying whether the scalar
value resulting from expr has a real
value. 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. Many operations return the
undefined value under exceptional conditions, such as end-of-file,
uninitialized variable, system error, and so on. 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.