The "shell" Linux shell if statement is detailed

If statement 1.1 if statement explanation

If is a judgment statement, if the action is similar to [], the general judgment is more or the execution of the statement is more, then will use if

1.2 If format

First format

if [ 判断条件 ];then    内容else    内容fi

Second form, multiple judgments

if [ 判断条件 ];then    内容elif [ 判断条件 ];then    内容else    内容fi

1.3 Precautions

There must be spaces on both sides of [] after the IF statement

1.4 If example

1.if judgment
Determine if/root/a.txt exists, if present, echo 0, if not present, Echo1

#!/bin/bash -if [ -f /root/a.txt ];then        echo 0else        echo 1fi

2.if...elif...else ...
Determine if/root/a.txt exists, if present, then echo A.txt, determine if/root/b.txt exists, if present, then echo B.txt, if a.txt and b.txt do not exist, then output error

#!/bin/bash -if [ -f /root/a.txt ];then        echo "a.txt"elif [ -f /root/b.txt ];then        echo "b.txt"else        echo "error"fi

The "shell" Linux shell if statement is detailed