How to use the Linux expr command

It is used to evaluate the value of expression variables in UNIX/LINUX. It is generally used as an integer or a string.

Syntax

Expr expression

Expression description:

• Separate each item with spaces;
• Place the slash (/) before a specific shell character;
• Enclose strings containing spaces and other special characters in quotation marks.

Instance

1. Calculate the string length

> Expr length "this is a test"

14

2. Capture strings

> Expr substr "this is a test" 3 5

Is

3. Capture the position where the first character numeric string appears

> Expr index "sarasara"

2

4. Integer operation

> Expr 14% 9

5

> Expr 10 + 10

20

> Expr 1000 + 900

1900

> Expr 30/3/2

5

> Expr 30/* 3 (when using a multiplication number, you must use a backslash to block its specific meaning. Because shell may misunderstand the meaning of the asterisk)

90

> Expr 30*3

Expr: Syntax error