Perl Undefined Value

In Perl, a variable is undefined when we declare it but not assign it to another value. Enabling strict and warnings, usage of a Perl Undefined Value will result in “Use of Uninitialized value $varname in concatenation or string…” warning. Intuitively, we must define every variable in our program. Therefore, we might want to compare a variable to Perl Undefined Value and Perl has built-in functions to help us with that.

Built-in “defined” and “undef” Functions

We use “defined” function for checking a variable’s defined situation. Additionally, we use “undef” function in order to set a value to undefined.

Best Perl practice is to enable strict and warnings in scripts. Never ignore Perl undefined value warnings. Usage of a Perl Undefined Value is usually an indicator of a serious error. In order to have clean program flow and data health, it is best to always use defined variables.

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