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?: Elvis Operator

Returns the right operand if the left operand is falsy (expression)

Description

The Elvis Operator is a little like a conditional where the result of the operation is the first non-falsy value from left to right.

A falsy value is any of the following:

• an unset / undefined variable
• any value with a null data type
• a str or generic with the value false, null, 0, no, off, fail, failed, or disabled
• a number (num, float or int) with the value 0
• an empty object or zero length array
• and, of course, a boolean with the value false

Examples

Assign with a default value

» $foo = $bar ?: "baz"

If $bar is falsy, then the value of $foo will be “baz”.

Multiple elvis operators

» $unset_variable ?: null ?: false ?: "foobar"
foobar

Detail

Whats in a name?

Wikipedia explains this best where it says:

The name “Elvis operator” refers to the fact that when its common notation, ?:, is viewed sideways, it resembles an emoticon of Elvis Presley with his signature hairstyle.

See Also

• Error String, strerr: err: Print a line to the stderr
• Expressions: expr: Expressions: mathematical, string comparisons, logical operators
• Operators And Tokens: All supported operators and tokens
• Output String, stdout: out: Print a string to the stdout with a trailing new line character
• Pipe Fail: trypipe: Checks for non-zero exits of each function in a pipeline
• Pipeline: Overview of what a “pipeline” is
• Schedulers: Overview of the different schedulers (or ‘run modes’) in Murex
• Try Block: try: Handles non-zero exits inside a block of code
• && And Logical Operator: Continues next operation if previous operation passes
• ?? Null Coalescing Operator: Returns the right operand if the left operand is empty / undefined (expression)
• ? stderr Pipe: Pipes stderr from the left hand command to stdin of the right hand command (removed 8.0)
• || Or Logical Operator: Continues next operation only if previous operation fails
• null: null function. Similar to /dev/null

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This document was generated from gen/expr/elvis-op_doc.yaml.