Linux command to delete file content

The '>' character is the shell (often Bash) redirection character. You are at a command prompt of the shell, probably Bash but you don't specify. The command as you have written basically says "redirect <nothing> to the file /AAA/BBB/CCC/DDD/main_copy.json". The net result is to truncate the file to zero length, effectively deleting its contents.

Since there are no spaces in the argument to '>', bash treats it as a single argument, thus there is no possibility that your command will delete contents of any files in any of the directories in your path. In any case, the '>' redirect operator does not work with multiple arguments. So if you were to say:

[user@yyy ~]$ > /AAA /BBB/CCC/DDD/main_copy.json

The net effect would issue an error because you can't redirect to a directory, only to a file. If you were to say:

[user@yyy ~]$ > /AAA/myfile.txt BBB/CCC/DDD/main_copy.json

the shell would truncate the file myfile.txt to zero length, (or create a zero-length file if it did not exist) and then treat the second argument as an executable command, which of course would fail with something like "Permission Denied" because it's not an executable.

Hope that helps. Bash (and other shells) is a complicated beast and takes years to really learn well.