Shell programming in Linux-conditional Testing

 

1.Test File status

Table 1 File status test

-D directory-s file length is greater than 0, not empty -F: regular file -L symbolic connection -R readable-x executable

-S file length is greater than 0, not empty -W writable -The U file has the s u I d bit setting. -X executable

 

2.Use logical operators during testing

-Logic A and the operators are true on both sides, and the result is true. Otherwise, the result is false.

-O logic or, if either side of the operator is true, the result is true. Otherwise, the result is false.

Example:

[-R t.txt-a-W t.txt]

Echo $?

0

 

3.String Testing

= Two strings are equal.

! = Two strings.

-Z empty string.

-N is a non-empty string.

Example:

Test-Z $ path

Echo $?

1

 

4.Test Value

-The EQ value is equal.

-The ne values are not equal.

-The first number of GT is greater than the second number.

-Lt: the first number is smaller than the second number.

-The first number of Le is less than or equal to the second number.

-The first number of Ge is greater than or equal to the second number.

Example:

[80-lt 100]

Echo $?

0

 

5. exprUsage:

Expr 10/* 10

100

Extpr 10/10

1