Bash 整数比较
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/14511295/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Bash integer comparison
提问by Cheiron
I want to write a bash script that checks if there is at least one parameter and if there is one, if that parameter is either a 0 or a 1. this is the script:
我想编写一个 bash 脚本来检查是否至少有一个参数，如果有一个，如果该参数是 0 或 1。这是脚本：
#/bin/bash
if (("$#" < 1)) && ( (("./setTouchpadEnabled: line 2: ((: ./setTouchpadEnabled != 1: syntax error: operand expected (error token is "./setTouchpadEnabled != 1")
./setTouchpadEnabled: line 2: ((: ./setTouchpadEnabled -ne 0q: syntax error: operand expected (error token is "./setTouchpadEnabled -ne 0q")
" != 1)) || (("#/bin/bash
if [[ ( "$#" < 1 ) || ( !( "" == 1 ) && !( "" == 0 ) ) ]] ; then
echo this script requires a 1 or 0 as first parameter.
else
echo "first parameter is "
xinput set-prop 12 "Device Enabled" #/bin/bash
if (( $# )) && (( == 0 || == 1 )); then
echo "first parameter is "
xinput set-prop 12 "Device Enabled" $ ./tmp.sh
this script requires a 1 or 0 as first parameter.
$ ./tmp.sh 0
first parameter is 0
$ ./tmp.sh 1
first parameter is 1
$ ./tmp.sh 2
this script requires a 1 or 0 as first parameter.
else
echo this script requires a 1 or 0 as first parameter.
fi
fi
" -ne 0q)) ) ; then
echo this script requires a 1 or 0 as first parameter.
fi
xinput set-prop 12 "Device Enabled" #/bin/bash
if (( ${1:-2} >= 2 )); then
echo "First parameter must be 0 or 1"
fi
# rest of script...
This gives the following errors:
这会导致以下错误：
$ ./test
First parameter must be 0 or 1
$ ./test 0
$ ./test 1
$ ./test 4
First parameter must be 0 or 1
$ ./test 2
First parameter must be 0 or 1
What am I doing wrong?
我究竟做错了什么？
采纳答案by user000001
This script works!
这个脚本有效！
(("$#" < 1)) && ( (("" != 1)) || (("" -ne 0q)) )
But this also works, and in addition keeps the logic of the OP, since the question is about calculations. Here it is with only arithmetic expressions:
但这也有效，并且还保留了 OP 的逻辑，因为问题是关于计算的。这里只有算术表达式：
(( "$#" < 1 && # If the number of arguments is less than one…
"" != 1 || "" -ne 0)) # …how can the first argument possibly be 1 or 0?
The output is the same1:
输出是相同的1：
(( "$#" )) && (( == 1 || == 0 )) # If true, there is at least one argument and its value is 0 or 1
[1] the second fails if the first argument is a string
[1] 如果第一个参数是字符串，则第二个失败
回答by koola
Easier solution;
更简单的解决方案；
case "" in
0|1) xinput set-prop 12 "Device Enabled" ;;
*) echo "This script requires a 1 or 0 as first parameter." ;;
esac
Output
输出
##代码##Explanation
解释
(( ))- Evaluates the expression using integers.${1:-2}- Uses parameter expansion to set a value of2if undefined.>= 2- True if the integer is greater than or equal to two2.
(( ))- 使用整数计算表达式。${1:-2}- 使用参数扩展来设置2如果未定义的值。>= 2- 如果整数大于或等于二，则为真2。
回答by kojiro
The zeroth parameter of a shell command is the command itself (or sometimes the shell itself). You should be using $1.
shell 命令的第零个参数是命令本身（或者有时是 shell 本身）。你应该使用$1.
Your boolean logic is also a bit confused:
你的布尔逻辑也有点混乱：
##代码##This is probably what you want:
这可能是你想要的：
##代码##回答by William
I know this has been answered, but here's mine just because I think case is an under-appreciated tool. (Maybe because people think it is slow, but it's at least as fast as an if, sometimes faster.)
我知道这已经得到了回答，但这是我的，因为我认为 case 是一个被低估的工具。（也许是因为人们认为它很慢，但它至少和 if 一样快，有时更快。）
##代码##