如何比较bash中的变量

Question

我是linux控制台中的乞丐；我想用整数变量创建if语句

if[$x= [$#-2]]

但是控制台收到如果can't find this statment if[1 = [5-2]]请帮助我和纠正我的陈述。

Answer 1

您需要算术扩展：$((expression))

if [ $x = $(($# - 2)) ]; then
# ^ ^  ^ ^           ^ spaces are mandatory

Answer 2

启动$#是传递给bash脚本的参数数

./bash_script 1 2 3

$#汽车-神奇地填充到3。我希望你已经知道这一点。

#!/bin/bash
x=1
#If you are trying to compare `$x` with the value of the expression `$# - 2` below is how you do it :
if (( $x == $# - 2 ))
then
echo "Some Message"
fi
#If you are trying to check the assignment to `$x was successful below is how you do it :
if (( x = $# - 2 ))
then
echo "Some Message"
fi

第二个条件几乎总是正确的，但第一个条件可能是假的。以下是我的测试结果：

#Here the both ifs returned true
sjsam@WorkBox ~/test
$ ./testmath1 1 2 3 
Some Message
Some Message
#Here the first if returned false because we passed 4 parameters
sjsam@WorkBox ~/test 
$ ./testmath1 1 2 3 4
Some Message