Perl Language True and false
Syntax
- undef # False
- '' # Defined, False
- 0 # Defined, Has Length, False
- '0' # Defined, Has Length, False
Remarks
Perl does not have a boolean data type, nor does it have any true and false keywords like many other languages. However, every scalar value will evaluate to true or false when evaluated in a boolean context (the condition in an if statement or a while loop, for example).
The following values are considered false:
'', the empty string. This is what the built-in comparison operators return (e.g.0 == 1)0, the number 0, even if you write it as 000 or 0.0'0', the string that contains a single 0 digitundef, the undefined value- Objects that use overloading to numify/stringify into false values, such as
JSON::false
All other values are true:
- any non-zero number such as
1,3.14,'NaN'or'Inf' - any string that is numerically 0 but not literally the string
'0', such as'00','0e0',"0\n"and"abc".
If you are intentionally returning a true numerically 0 value, prefer'0E0'(used by well known modules) or'0 but true'(used by Perl functions) - any other string that is not empty, such as
' ','false' - all references, even if they reference false values, such as
\'',[], or{} - an array or hash of false values
The following operators are commonly treated to return a boolean in scalar context:
-
@areturns whether the array is empty or not -
%hreturns whether the hash is empty or not -
grepreturns whether any matching items were found or not -
@a = LISTand(LIST) = LISTreturn whether the right-hand side LIST produced any scalars or not
