Linux Gvim shell if...else语句

#if else语句,共分三种：if...fi ; if ...else ...fi ; if ...elif...else...fi
#if else fi 语句语法
#if [ expression ]
#then
#    Statement to be executed if expression is true
#else
#    Statement to be executed if expression is not true
#fi
#if elif else fi语句语法：哪一个expression为true就执行哪一个语句，如果全是false则执行else语句
#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

a=30
b=20
if [ $a == $b ]
then
   echo "a is equal to b"
elif [ $a -gt $b ]
then
   echo "a is greater than b"
elif [ $a -lt $b ]
then
   echo "a is less than b"
else
   echo "None of the condition met"
fi

#if else 语句也可以写成一行，以命令的方式运行，如下：

if test $[ 2*3 ] -eq $[ 1+5 ] ;then echo "true" ; fi

#if else 语句也经常与test命令结合使用
#test命令用于检查某个条件是否成立与 []类似

num1=$[2*3]
num2=$[1+5]
if test ${num1} -eq ${num2}
then
    echo 'The two numbers are equal!'
else
        echo 'The two numbers are not equal!'
fi