Linux conditional judgment: eq, NE, GT, lt, GE, le

Introduction to Commands:

Condition Judgment:

If the user does not exist

Add user, give password and display add success;

otherwise

Show if no already in, no add;

Variable name:

1 , can contain only letters, numbers, and underscores, and cannot begin with numbers;

2 , should not be the same as the existing environment variables in the system;

3 , it is best to see the name and know righteousness;

Bash how to achieve the conditional judgment?

Condition Test Type:

integer test

character Test

file Test

Expressions for Conditional tests:

[Expression]

[[Expression]]

Test Expression       

Integer comparison:

-eq: tests whether two integers are equal, such as $A-eq $B

-ne: test whether the two integers are unequal, unequal, true, equal, false;

-GT: tests whether one number is greater than the other, greater than, true, or false;

-lt: tests whether one number is less than the other, less than, true; otherwise, false;

-ge: greater than or equal to

-le: Less than or equal to

The logical relationship between commands:

logic and: &&

When the first condition is false, the second condition is no longer judged and the final result is already there;

When the first condition is true, the second condition must be judged;

logical OR : | |    

4 . Command instance:

If the user User6 does not exist, the user is added User6

! ID USER6 && useradd user6

ID User6 | | Useradd User6

If the number of rows in the/etc/inittab file is greater than 100, a large file is displayed;

[' Wc-l/etc/inittab | cut-d '-f1 '-gt] && echo "Large file."  

If the user exists, the user is already present, otherwise the user is added;

ID user1 && echo "user1 exists." | | Useradd user1

If the user does not exist, add; otherwise, show that it already exists;

! ID user1 && Useradd user1 | | echo "User1 exists."

If the user does not exist, add and give the password, otherwise, show that it already exists;

! ID user1 && useradd user1 && echo "user1" |passwd--stdin User1 | | echo "User1exists."

This article is from the "Learn Linux history" blog, please be sure to keep this source http://woyaoxuelinux.blog.51cto.com/5663865/1863256

Linux conditional judgment: eq, NE, GT, lt, GE, le