Shell script Programming--if statements

How to handle the programming logic:
1, sequential execution
2, select Execute
3, loop execution

Conditional Select if statement
Select Execute:
Note: If statements can be nested

Single Branch
if judgment condition; then
Branch code with true condition
Fi

Example code:

1 #!/bin/bash
2
3 #Author: Wangjun
4 #Version: 1.0
5 #Create time:2016-08-13 19:40:55
6 #Description: Ifsingle test
7
8 Read-p "Please input a username:" Name
9 If ID $name &>/dev/null; then
echo "$name user exists,user ID: ' Id-u $name '"
One fi

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Dual Branch
if judgment condition; then
Branch code with true condition
Else
The condition is a false branch code
Fi

Example code:

1 #!/bin/bash
2
3 #Author: Wangjun
4 #Version: 1.0
5 #Create time:2016-08-13 20:00:00
6 #Description: Ifdouble test
7
8 Read-p "Please input a username:" Name
9 If ID $name &>/dev/null; then
echo "$name user exists,user ID: ' Id-u $name '"
One else
echo "$name user doesn ' t exist"
Fi

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Multi-Branch
if CONDITION1; Then
If-true
Elif CONDITION2; Then
If-ture
Elif CONDITION3; Then
If-ture
...
Else
All-false
Fi

Judge by condition, when the first encounter is a "true" condition, execute its branch, and then end the entire if statement

This article is from the "Love Firewall" blog, be sure to keep this source http://183530300.blog.51cto.com/894387/1837637

Shell script Programming--if statements