Linux expr Command

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

Syntax

expr expression

Expression Instructions:

Separate each term with a space;
Use a backslash \ before shell-specific characters;
Enclose strings containing spaces and other special characters in quotes.

Examples

Calculate string length
```
> expr length "this is a test"
14
```

Extract substring

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

Find the position of the first occurrence of a character in a string
```
> expr index "sarasara" a
2
```

Integer operations

> expr 14 % 9
5
> expr 10 + 10
20
> expr 1000 + 900
1900
> expr 30 / 3 / 2
5
> expr 30 \* 3 (Use a backslash to mask the special meaning of the asterisk, as the shell might misinterpret the asterisk)
90
> expr 30 * 3
expr: Syntax error

Linux Command Manual

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