let

Evaluate arithmetic expressions.

Source: src/execution/builtins.f90

Synopsis

let expression [expression ...]

Description

The let builtin evaluates arithmetic expressions. It's equivalent to (( expression )) but allows multiple expressions.

Usage

Basic Arithmetic

let "a = 5 + 3"
echo $a    # 8

let "b = a * 2"
echo $b    # 16

Multiple Expressions

let "x = 1" "y = 2" "z = x + y"
echo $z    # 3

Without Quotes

let a=5
let b=a+3
echo $b    # 8

Operators

Examples

Counter

let count=0
let count++
let count++
echo $count    # 2

Calculations

let "result = (5 + 3) * 2"
echo $result   # 16

let "power = 2 ** 10"
echo $power    # 1024

Conditional

let "x = 5"
let "y = (x > 3) ? 1 : 0"
echo $y    # 1

Bitwise

let "flags = 0"
let "flags |= 1"      # Set bit 0
let "flags |= 4"      # Set bit 2
echo $flags           # 5

let "flags &= ~1"     # Clear bit 0
echo $flags           # 4

Comparison with (( ))

# Equivalent expressions
let "x = 5 + 3"
(( x = 5 + 3 ))
x=$((5 + 3))

# let allows multiple in one command
let "a=1" "b=2" "c=a+b"

Exit Status

let "5 > 3"
echo $?    # 0 (true)

let "3 > 5"
echo $?    # 1 (false)

Notes

• Spaces require quoting: let "a = 5" not let a = 5
• Variables don't need $: let "a = b + 1"
• Leading zeros mean octal: let "x = 010" is 8
• 0x prefix for hex: let "x = 0xff" is 255

See Also

• Expansion - Arithmetic expansion
• test - Conditional tests