Logical AND

The && (logical AND) operator is a control operator used to chain commands based on their exit status. It implements short-circuit evaluation, executing the right-hand command strictly if, and only if, the left-hand command terminates with an exit status of zero (success).

command1 && command2

Execution Mechanics

Bash parses the entire command line or script block for syntax before any execution begins. If no syntax errors are found, execution proceeds as follows:

1. Bash executes command1 and captures its exit status ($?).
2. If the exit status is 0 (success), Bash proceeds to execute command2.
3. If the exit status is non-zero (1-255, indicating failure), Bash short-circuits the evaluation. command2 is not executed.

Exit Status Propagation

The overall exit status of an && command list is determined by the last command executed within that list:

• If command1 fails, the list returns the non-zero exit status of command1.
• If command1 succeeds, the list returns the exit status of command2, regardless of whether command2 succeeds or fails.

Interaction with errexit (set -e)

When the errexit option (set -e) is enabled, Bash normally exits immediately if a command yields a non-zero exit status. However, according to POSIX and Bash semantics, the errexit rule is ignored for any command in an AND-OR list except the last one. Consequently, if command1 fails, the overall && list returns a non-zero exit status, but this does not trigger set -e to halt the script. The script will only terminate if the final command in the chain (e.g., command2) is executed and fails.

Associativity and Chaining

The && operator is left-associative and shares equal precedence with the || (logical OR) operator. When chaining multiple commands, evaluation proceeds strictly from left to right.

command1 && command2 && command3

In this sequence, command3 is executed only if both command1 and command2 sequentially return an exit status of 0. A non-zero exit status at any point breaks the chain immediately.

Contextual Overloading

Beyond operating as a command list control operator, && is overloaded in specific Bash evaluation contexts:

• Extended Test Construct ([[ ]]): Acts as a logical AND operator between conditional expressions. It evaluates the results of specific conditional test operators (such as string comparisons, -z, or -f), rather than generic boolean “truthiness”.

[[ expression1 && expression2 ]]

* **Arithmetic Evaluation (`(( ))`):** Acts as a logical AND operator for integer arithmetic. If both expressions evaluate to non-zero integers, the arithmetic expression evaluates to the integer value `1`. This resulting non-zero integer causes the `(( ))` compound command to terminate with an exit status of `0` (success). Conversely, if the arithmetic expression evaluates to the integer `0`, the compound command terminates with an exit status of `1` (failure).
  ```bash
(( integer1 && integer2 ))

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