2017网站建设前景,旅游网站建设项目规划书,asp公司网站,韩国怎样才能出线if 语句通过关系运算符判断表达式的真假来决定执行哪个分支。Shell 有三种 if ... else 语句#xff1a; if ... fi 语句#xff1b;if ... else ... fi 语句#xff1b;if ... elif ... else ... fi 语句。1) if ... else 语句 if ... else 语句的语法#xff1a; if [ ex…if 语句通过关系运算符判断表达式的真假来决定执行哪个分支。Shell 有三种 if ... else 语句 if ... fi 语句if ... else ... fi 语句if ... elif ... else ... fi 语句。1) if ... else 语句 if ... else 语句的语法 if [ expression ]
thenStatement(s) to be executed if expression is true
fi 如果 expression 返回 truethen 后边的语句将会被执行如果返回 false不会执行任何语句。最后必须以 fi 来结尾闭合 iffi 就是 if 倒过来拼写后面也会遇见。注意expression 和方括号([ ])之间必须有空格否则会有语法错误。举个例子 #!/bin/sh a10b20 if [ $a $b ]then echo a is equal to bfi if [ $a ! $b ]then echo a is not equal to bfi 运行结果 a is not equal to b 2) if ... else ... fi 语句 if ... else ... fi 语句的语法 if [ expression ]
thenStatement(s) to be executed if expression is true
elseStatement(s) to be executed if expression is not true
fi 如果 expression 返回 true那么 then 后边的语句将会被执行否则执行 else 后边的语句。举个例子 #!/bin/sh a10b20 if [ $a $b ]then echo a is equal to belse echo a is not equal to bfi 执行结果 a is not equal to b 3) if ... elif ... fi 语句 if ... elif ... fi 语句可以对多个条件进行判断语法为 if [ expression 1 ]
thenStatement(s) to be executed if expression 1 is true
elif [ expression 2 ]
thenStatement(s) to be executed if expression 2 is true
elif [ expression 3 ]
thenStatement(s) to be executed if expression 3 is true
elseStatement(s) to be executed if no expression is true
fi 哪一个 expression 的值为 true就执行哪个 expression 后面的语句如果都为 false那么不执行任何语句。举个例子 #!/bin/sh a10b20 if [ $a $b ]then echo a is equal to belif [ $a -gt $b ]then echo a is greater than belif [ $a -lt $b ]then echo a is less than belse echo None of the condition metfi 运行结果 a is less than b if ... else 语句也可以写成一行以命令的方式来运行像这样 if test $[2*3] -eq $[15]; then echo The two numbers are equal!; fi; if ... else 语句也经常与 test 命令结合使用如下所示 num1$[2*3]num2$[15]if test $[num1] -eq $[num2]then echo The two numbers are equal!else echo The two numbers are not equal!fi 输出 The two numbers are equal! test 命令用于检查某个条件是否成立与方括号([ ])类似。转载于:https://www.cnblogs.com/yang-hao/p/5969252.html
