Linux expr command

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The expr command is a manual command-line counter used to calculate the value of expression variables under UNIX/LINUX, generally used for integer values, but can also be used for strings.

Syntax

expr Expression

Expression Description:

• Separate each item with a space;

• Use a backslash \ before shell-specific characters;

• Use quotes to enclose strings containing spaces and other special characters

Online Examples

1. Calculate the length of the string

> expr length "this is a test"
　14

2. Capture the string

> expr substr "this is a test" 3 5
is is

3. Capture the position of the first character string occurrence

> expr index "sarasara" a
　2

4. Integer Arithmetic

　> expr 14 % 9
　5
　> expr 10 + 10
　20
　> expr 1000 + 900
　1900
　> expr 30 / 3 / 2
　5
　> expr 30 * 3 (It is necessary to use a backslash to shield the specific meaning of the asterisk when using the multiplication sign. Because the shell may misunderstand the meaning of the asterisk displayed)
　90
　> expr 30 * 3
　expr: Syntax error

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