How to generate date string with shell command

Sometimes we need to generate date string, the shell command default format can brings us somewhere, but how about the date with format 20-05-10?
We can print date string using shell command date with format flags.

date +%y-%m-%d
for example will print today's date in short format as
20-05-13

sometimes, the generate date strings can be used to construct other shell commands with ``.
The date command wrapping inside `` will get executed first, the result string then concatenated with the rest of the strings to form a shell command.

For example, when the following command is executed

echo filename.`date +%y-%m-%d`.log

`date +%y-%m-%d` will execute first, generate a string 20-05-13. Then string 20-05-13 is concatenated with rest of the command to get a new shell command:

echo filename.20-05-13.log

the above command's running result is
filename.20-05-13.log

 

=================
demo>date
Wed May 13 15:05:10 EDT 2020
demo>date +%y-%m-%d
20-05-13
demo>echo filename.`date +%y-%m-%d`.log
filename.20-05-13.log
==================

Similarly, we can use the same technique to construct more sophisticated grep shell command:

ls myapp.`date +%y-%m-%d`*.log | xargs -I {} cat{} | grep -i 'exception\|error' -A 2 -B 2

the above command, list all myapp log files generated today. Among though files, we search for exception and error messages, print out the line with 2 lines before and 2 lines after.