Touching a file (changing last updated Date/time) with the COPY command. Here's how and a little history too.

The Old New Thing - Why is the syntax for touching a file from the command prompt so strange?

The magic incantation for updating the last-modified date on a file is

COPY /B FILE+,,

What strange syntax! What's with the plus sign and the commas, anyway?

The formal syntax is the much more straightforward

COPY /B A+B+C+D

This means to start with the file A, then append the files B, C, and D, treating them all as binary files.

If you omit the B+C+D part, then you get ...

COPY /B A+

This means "Start with A, then append nothing." The side effect is that the last-write time gets updated, because the command processor opens A for append, writes nothing, then closes the handle.

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As you know, I love these kinds of posts. First off I didn't know you could even do this with the COPY command, secondly I had to laugh that he tried it on MS-DOS versions all the way back to 2.1 and finally the reminder that backward compatibility can be a...