Appending an extension to a new file created with xcopy

Question

I've been having problems with xcopy in the past few days, and I'd like to stop ripping out my hair. In my DOS class, a portion of an assignment requires a file to be copied (with xcopy), and the new file name should have .bak appended, while keeping the original extension, but I can't get it to do this properly. Using xcopy * *.bak, I would expect it to do this, but it replaces the file extension, instead of appending. A friend of mine in the same class says this works as it should for him, which I do find strange. I've also tried other combinations of wildcards that Google results have suggested, but they give me the same results, and that's if I can find anything else relating to this.

I'd like to also expand, I'm not asking for homework help. My homework is easy, but I don't understand why xcopy would give me these results when the same command works for someone else. Thanks.

Answer 1

in DOS (and Windows command line) mask for all-files is *.*. Like in "files always have an extension, sometimes it's empty string". And filenames cannot end with .

So mask * canonically mean "files with empty extension". But some utilities, including xcopy as you found, automagically expand * to *.* because… well, I seek no logic when there isn't one. So * is shortcut for *.* in some cases.

Also, xcopy is apparently too smartass, and replaces extension even with

xcopy *.* *.*.bak

to add .bak extension, use plain copy with

copy * *.*.bak

(note that copy * *.bak will still replace extension)

or, if you required to use xcopy, write for-loop.

FOR %%I IN (*.*) DO xcopy %%I "%%~I.bak"

(in an interactive command line, use single percent-signs % instead of %%)