if...fi语法

if [ expression ]
then
 Statement(s) to be executed if expression is true
fi​

注：expression左右有空格，最后必须以fi结尾。

if...else...fi语法

if [ expression ]
then
   Statement(s) to be executed if expression is true
else
   Statement(s) to be executed if expression is not true
fi

if...elif...fi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

#!/bin/bash

a=10
b=10
if [ $a -lt $b ]
then
    echo "a lesser than b"
elif [ $a -eq $b ]
then
    echo "a equal to b"
else
    echo "a greater to b"
fi

作者：Gacfox
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