if.elif.fi语句是控制语句的一级高级形式，它允许Shell在多个条件中做出正确的决定。
If-elif - 语法
if [ expression 1 ] then Statement(s) to be executed if expression 1 is true elif [ expression 2 ] then Statement(s) to be executed if expression 2 is true elif [ expression 3 ] then Statement(s) to be executed if expression 3 is true else Statement(s) to be executed if no expression is true fi
这段代码只是一系列if语句，其中每个if都是上一条语句的else子句的一部分。这里的语句是基于TRUE条件执行的，如果没有一个条件为TRUE，则执行else块。
If-elif - 示例
#!/bin/sha=10 b=20
if [ b ] then echo "a is equal to b" elif [ b ] then echo "a is greater than b" elif [ b ] then echo "a is less than b" else echo "None of the condition met" fi
执行后，您将收到以下输出-
a is less than b
