Linux 多个 -a 大于/小于 break bash 脚本
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Multiple -a with greater than / less than break bash script
提问by Calvin Froedge
I wrote a bash script that performs a curl call only during business hours. For some reason, the hourly comparison fails when I add an "-a" operator (and for some reason my bash does not recognize "&&").
我写了一个 bash 脚本，它只在工作时间执行 curl 调用。出于某种原因，当我添加“-a”运算符时，每小时比较失败（并且由于某种原因，我的 bash 无法识别“&&”）。
Though the script is much larger, here is the relevant piece:
虽然脚本要大得多，但这里是相关的部分：
HOUR=`date +%k`
if [ $HOUR > 7 -a $HOUR < 17 ];
then
//do sync
fi
The script gives me the error:
该脚本给了我错误：
./tracksync: (last line): Cannot open (line number): No such file
However, this comparison does not fail:
但是，这种比较并没有失败：
if [ $DAY != "SUNDAY" -a $HOUR > 7 ];
then
//do sync
fi
Is my syntax wrong or is this a problem with my bash?
我的语法错误还是我的 bash 有问题？
采纳答案by Costi Ciudatu
You cannot use <and >in bash scripts as such. Use -ltand -gtfor that:
您不能在 bash 脚本中使用<和>。为此使用-lt和-gt：
if [ $HOUR -gt 7 -a $HOUR -lt 17 ]
<and >are used by the shell to perform redirection of stdin or stdout.
<并且>被 shell 用来执行 stdin 或 stdout 的重定向。
The comparison that you say is working is actually creating a file named 7in the current directory.
您所说的比较有效实际上是创建一个7在当前目录中命名的文件。
As for &&, that also has a special meaning for the shell and is used for creating an "AND list" of commands.
至于&&，这对 shell 也有特殊含义，用于创建命令的“AND 列表”。
The best documentation for all these: man bash(and man testfor details on comparison operators)
所有这些的最佳文档：（man bash以及man test有关比较运算符的详细信息）
回答by Simon Richter
I suggest you use quotes around variable references and "standard" operators:
我建议您在变量引用和“标准”运算符周围使用引号：
if [ "$HOUR" -gt 7 -a "$HOUR" -lt 17 ]; ...; fi
回答by dogbane
Try using [[instead, because it is safer and has more features. Also use -gtand -ltfor numeric comparison.
尝试[[改用，因为它更安全且功能更多。还可以使用-gt并-lt进行数值比较。
if [[ $HOUR -gt 7 && $HOUR -lt 17 ]]
then
# do something
fi
回答by jordanm
There are a few answers here but none of them recommend actual numerical context.
这里有一些答案，但没有一个推荐实际的数字上下文。
Here is how to do it in bash:
以下是如何在 bash 中执行此操作：
if (( hour > 7 && hour < 17 )); then
...
fi
Note that "$" is not needed to expand variables in numerical context.
请注意，在数字上下文中扩展变量不需要“$”。
