Overview
The expr command is used to perform arithmetic, relational, logical, and string operations. Each argument is treated as a separate token, so spaces are required between operators and operands.
Key Features
- Arithmetic operations (addition, subtraction, multiplication, division, modulo)
- String operations (length, substring, index, regular expression matching)
- Relational operations (equal to, not equal to, greater than, less than)
- Logical operations (AND, OR)
Main Operators
The expr command uses various operators to evaluate expressions. Each operator must be treated as a separate argument.
Arithmetic Operators
Relational Operators
Logical Operators
String Operators
Generated command:
Try combining the commands.
Description:
`expr` Executes the command.
Combine the above options to virtually execute commands with AI.
Usage Examples
Basic Arithmetic Operation
expr 10 + 5Adds two numbers.
Multiplication with a Variable
num=20
expr $num \* 3Performs multiplication using a variable's value. The multiplication operator (*) has a special meaning in the shell and must be escaped.
Getting String Length
expr length "Hello World"Returns the length of a given string.
Extracting a Substring
expr substr "example" 3 4Extracts 4 characters from the string 'example' starting at the 3rd position.
Regular Expression Matching and Extraction
expr "filename.tar.gz" : ".*\.\(tar\.gz\)"Extracts the part of the string that matches the regular expression. Content within parentheses is returned as a submatch.
Logical AND Operation
expr 5 \& 0Returns the first operand if both operands are non-zero. The ampersand (&) has a special meaning in the shell for background execution and must be escaped.
Tips & Precautions
Points to note and useful tips when using expr.
Key Precautions
- **Spaces are Mandatory**: Always include spaces between operators and operands.
- **Escaping**: Characters that have special meaning in the shell (e.g., `*`, `(`, `)`, `&`, `|`, `<`) must be escaped with a backslash (`\`) or enclosed in quotes.
- **Integer Operations**: `expr` primarily supports integer operations. For floating-point arithmetic, use other tools like `bc`.
- **Storing Results**: The output of `expr` is sent to standard output. To store the result in a shell variable, use command substitution (e.g., `result=$(expr 10 + 5)` or `result=`expr 10 + 5``).