|= operator in Bash is the bitwise inclusive OR assignment operator. It performs a bitwise OR operation between a variable (the left-hand side operand) and an evaluated expression (the right-hand side operand), and immediately assigns the resulting integer back to the variable.
Syntax
Because Bash variables are untyped strings by default, the|= operator must be executed within an arithmetic evaluation context.
let builtin:
Mechanics
- Operand Evaluation: The right-hand side expression is fully evaluated as an integer.
- Bitwise OR (
|): Bash converts both the current value of the variable and the evaluated right-hand side into their underlying binary representations (typically 64-bit signed integers, depending on the system architecture). It then compares them bit by bit. If a bit is1in either operand, the corresponding bit in the result is set to1. It is set to0only if both bits are0. - Assignment (
=): The final binary result is converted back to a base-10 integer and assigned to the left-hand side variable.
Equivalence
The compound assignment|= is strictly syntactic sugar for a standard bitwise OR operation followed by an assignment:
Evaluation Example
When the operator is applied, the operation occurs at the binary level:Operator Precedence
In Bash arithmetic, the|= operator shares the second-lowest precedence level with other assignment operators (such as =, +=, &=, etc.), sitting strictly above the comma operator (,), which has the lowest precedence. Assignment operators evaluate right-to-left. Consequently, the entire right-hand side expression is evaluated before the bitwise OR assignment takes place.
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