How to use cat to combine files in Makefile?

Question

First of all, I am not at all sure whether this is the correct place to ask a question like this but...

I am currently working on a directory and trying to create a file which would contain all of the contents of the files of the directory. The requirement is that I have to do this by using a rule in a Makefile. Currently, my makefile has a list of the files at the top, then a few other rules and then my sad attempt of a rule. The issue I'm running into is that I constantly get the "no rule to make target x needed by y". I think the issue is with either my recipe or my prerequisites. So:

FILES= file1 file2 file3 file4 file5...

directory_name/all.txt: **HERE IS THE PART IDK ABOUT**
   cat $^ > $@

I'm very new to the make command and to coding in general for that matter, so it may be that this is a silly problem to have but still, I couldn't find any satisfying answers online elsewhere. I have been trying to either refer to the files via their directory (like directory_name/%.txt or something) or by just listing the files as the prerequisites but nothing has worked.

Answer 1

Your rule could look like

directory_name/all.txt: $(FILES)
        cat $(FILES) > $@

This would provide maximum portability so that the rule would work with both GNU make and BSD make (which may not understand $^; you don't say which implementation you're using). Note that the line with the cat command needs to be indented with a tab character.

Answer 2

The dependency list is just $(FILES).

Basically, that just expands the list named. So the target is remade if any of the files that contribute to its validity are newer that the target itself.

There is a shorthand that will wildcard files, if you have a pattern. For your example, probably just:

FILES= file[1-9]