Built-in judgment of linux shell and built-in judgment of linuxshell

Built-in judgment of linux shell and built-in judgment of linuxshell

Built-in judgment: 0 is returned when the result is successful, and non-zero is returned if the result is unsuccessful.

Test judgment Expression

[Judgment Expression] note that spaces must be left before and after the expression.

Numeric operation

-Eq equals

-Ne is not equal

-Gt greater

-Ge is greater than or equal

-Lt is less

-Le is less than or equal

String operation

= Equal

! = Not equal

-Is z empty?

-N is not empty

File Operations

-Whether r exists and is readable

-W exists and can be written

-Whether x exists and can be executed

-F: whether the file exists

-D whether this directory exists