let

let expression...

let is a Bash (and ksh) built-in that evaluates one or more arithmetic expressions. Each expression is evaluated using the same rules as `$(( ... ))`: integer math, C-style operators, and shell variable references without the leading `$`.The exit status is 0 if the value of the last evaluated expression is non-zero, and 1 if it is zero. This makes `let` usable in `if`/`while` conditions but is the inverse of typical command exit semantics — a successful arithmetic result of 0 (e.g., `let "x = 0"`) reports failure.

EXPRESSION

Arithmetic expression(s).

+, -, *, /, %, ** (power)

++, -- (increment/decrement)

==, !=, <, >, <=, >=

&&, ||, !

Bash/ksh built-in; not available in POSIX `sh` or `dash`. Integer arithmetic only — use `bc` or `awk` for floating point. The `(( ... ))` arithmetic command is generally preferred in modern Bash because it does not require quoting and has cleaner exit semantics. Returns exit code 1 when the final expression evaluates to 0, which can trigger `set -e` exits unexpectedly.

let is a Bash built-in command for arithmetic evaluation, similar to expr but more powerful.

bash(1), expr(1), bc(1)