使用参数变量在 bash 脚本中获取 X 天前的日期
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Getting date of X days ago in bash script, using argument variable
提问by Kof
I'm trying to calculate the date for a dynamic number of days ago in a bash script.
我正在尝试在 bash 脚本中计算动态天数前的日期。
This is what I've done -
这就是我所做的-
#!/bin/bash
STAMP=`date --date=' day ago' +%y%m%d`
but when running myscript 2, it says -
但是在运行时myscript 2，它说-
date: invalid date ` day ago'
How can I use my argument value in this formula?
我如何在这个公式中使用我的参数值？
回答by Kof
It works if ' is replaced with " into this command on the script -
如果在脚本中将 ' 替换为 " 到此命令中，它会起作用 -
STAMP=`date --date=" day ago" +%y%m%d`
The clue was the two different character ` and ' used in the error response -
线索是错误响应中使用的两个不同字符 ` 和 ' -
date: invalid date ` day ago'
An expert in bash scripting (not me) can probably explain why this has happen.
bash 脚本专家（不是我）可能会解释为什么会发生这种情况。
回答by devnull
It's because variable substitution wouldn't happen in single quotes, i.e. '$1'wouldn't expand but "$1"would.
这是因为变量替换不会发生在单引号中，即'$1'不会扩展但"$1"会。
As such, saying
如此，说
STAMP=`date --date=" day ago" +%y%m%d`
or
或者
STAMP=$(date --date=" day ago" +%y%m%d)
would work.
会工作。
