?? Null Coalescing OperatorReturns the right operand if the left operand is empty / undefined (expression)
The Null Coalescing operator is a little like a conditional where the result of the operation is the first non-empty value from left to right.
An empty value is any of the following:
null data typeOther “falsy” values such as numerical values of 0, boolean false, zero length strings and strings containing "null" are not considered empty by the null coalescing operator.
» $foo = $bar ?? "baz"If $bar is unset then the value of $foo will be “baz”.
» $unset_variable ?? null ?? "foobar"
foobarThe following extract was taken from Wikipedia:
The null coalescing operator (called the Logical Defined-Or operator in Perl) is a binary operator that is part of the syntax for a basic conditional expression in several programming languages. While its behavior differs between implementations, the null coalescing operator generally returns the result of its left-most operand if it exists and is not null, and otherwise returns the right-most operand. This behavior allows a default value to be defined for cases where a more specific value is not available.
In contrast to the ternary conditional if operator used as
x ? x : y, but like the binary Elvis operator used asx ?: y, the null coalescing operator is a binary operator and thus evaluates its operands at most once, which is significant if the evaluation ofxhas side-effects.
err): Print a line to the stderrexpr): Expressions: mathematical, string comparisons, logical operatorsis-null): Checks if a variable is null or undefinedout): Print a string to the stdout with a trailing new line charactertrypipe): Checks for non-zero exits of each function in a pipelinetry): Handles non-zero exits inside a block of code&& And Logical Operator: Continues next operation if previous operation passes?: Elvis Operator: Returns the right operand if the left operand is falsy (expression)? stderr Pipe: Pipes stderr from the left hand command to stdin of the right hand command (DEPRECATED)|| Or Logical Operator: Continues next operation only if previous operation failsThis document was generated from gen/expr/null-coalescing-op_doc.yaml.
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