“日期”命令中的“+”有什麼作用？

以下給了我一個日期：

$ date +%Y%m%d                                                                             
20201012 

這不會：

$ date %Y%m%d
date: invalid date ‘%Y%m%d’

手冊頁說+前面有FORMAT. +除了正確的語法之外還有什麼重要性？

date [OPTION]... [+FORMAT]

來自info date：

If given an argument that starts with a ‘+’, ‘date’ prints the
current date and time (or the date and time specified by the ‘--date’
option, see below) in the format defined by that argument, which is
similar to that of the ‘strftime’ function.  Except for conversion
specifiers, which start with ‘%’, characters in the format string are
printed unchanged.  The conversion specifiers are described below.

例如，您可以這樣做：

date +"The year is %Y"
The year is 2020

+引入了日期格式字元串。

引用自：https://unix.stackexchange.com/questions/614208