let - macOS


The let command in macOS is a powerful tool for assigning values to variables, modifying existing values, and performing basic arithmetic operations. It plays a vital role in shell scripting by allowing users to manipulate and store data dynamically.


let <variable>=<value>
let <variable>=<arithmetic expression>


  • <variable> is the name of the variable to be assigned a value.
  • <value> is the value to be assigned to the variable.
  • <arithmetic expression> is a mathematical expression that evaluates to a numerical value.


| Option | Description |
| = | Assigns a value to a variable. |
| += | Adds a value to an existing variable. |
| -= | Subtracts a value from an existing variable. |
| *= | Multiplies an existing variable by a value. |
| /= | Divides an existing variable by a value. |
| %= | Computes the modulus of an existing variable by a value. |


Simple Assignment:

let my_name="John Doe"

Arithmetic Operations:

let age=30
let age+=5
echo $age  # Outputs 35

Complex Arithmetic Expression:

let result=(5 * (4 + 3)) / 2

Common Issues

  • Uninitialized Variables: Ensure that variables are initialized before using them in arithmetic expressions.
  • Invalid Arithmetic: Verify that arithmetic expressions are syntactically correct and use valid operators.
  • Data Type Mismatches: Assign appropriate data types to variables to avoid errors during arithmetic operations.


The let command can be integrated with other macOS commands to create powerful scripts. For example:

let file_count=$(find . -type f | wc -l)
echo "Total files: $file_count"
  • expr – Evaluates arithmetic expressions.
  • declare – Declares and initializes variables.
  • read – Reads user input into variables.