expr

The expr command line tool is a utility in Unix-like operating systems that evaluates and prints the value of an expression. It is commonly used to perform basic arithmetic operations, string manipulation, and logical comparisons within shell scripts or directly from the command line. Some key features of expr include: 1. Arithmetic operations: expr can perform addition, subtraction, multiplication, and division on numbers. 2. String manipulation: It can extract substrings, match regular expressions, and concatenate strings. 3. Logical comparisons: expr allows you to perform comparisons such as equality, inequality, greater than, and less than between numbers or strings. 4. Conditional expressions: It supports basic if-else style conditions, enabling executing different code paths based on the expression's evaluation. 5. Error handling: expr handles potential errors like division by zero or invalid operands by returning appropriate error codes. Here's a simple example demonstrating the usage of expr: $ expr 5 + 3 8 $ expr length "Hello, World!" 13 $ expr substr "This is a test" 6 2 is $ expr index "abcdefg" "g" 7 $ expr \( 2 + 3 \) \* 4 20 In addition to these basic operations, expr can be combined with other command line utilities and control flow constructs to build more complex scripts or one-liners.