shell single branch if statement

A single branch if conditional statement

if [conditional judgment];then

program

be

or

if [conditional judgment]

then

program

be

 

Two grammar analysis

1. The if statement ends with fi, which is different from the curly brackets used in general languages.

2. [Conditional judgment] is to use the test command to judge, so there must be a space between the brackets and the conditional judgment.

3. The program to be executed after the condition is followed by then can be placed after [] and separated by ";". You can also write in a newline, you don't need to use ";".

 

Three examples

#!/bin/bash

test=$(env | grep USER |cut -d "=" -f 2)

if [ "$test" == "root" ]

then

echo "you are root"

be

 

Four running results

you are root

 

Five judgments of partition utilization

#!/bin/bash

rate=$(df -h|grep "/dev/sda3"|awk '{print $5}'|cut -d "%" -f1)

if [ $rate -le 80 ]

then

echo "/dev/sda3 is not full"

be

 

Six running results

/dev/sda3 is not full