If you are using Linux or some kind of Unix you may have noticed the command touch.
touch [-acm] [-r file] [-t [[CC]YY]MMDDhhmm[.SS]] file [...]
Mostly, it is used to create empty files, e.g. to create an empty file called new.txt:
But it can do much more! Originally it was build to manipulate the modification and access time of files. E.g. if you want to trick make to recompile a project just touch a file: