Cat with wildcard

Question

The question is maybe trivial but I can't get it to work. I just want to merge 2 particular files present in multiple specific folders into a new single file again in each specific folder.

cat */folder_*/*/file.a */folder_*/*/file.b > */folder_*/*/file.c

but it does not work 'cause

-bash: */folder_*/*/file.c: No such file or directory

So I thought maybe for some reason cat can't create files (though it does), so I tried

touch */folder_*/*/file.c; cat */folder_*/*/file.a */folder_*/*/file.b > */folder_*/*/file.c

but again it does not work with cat or even touch.

Answer 1

You can't use globbing for a destination file. You must fully specify the filename. It has nothing to do with cat specifically.

Answer 2

Maybe you want something like this;

for a in  */folder_*/*/file.a; do
    # maybe continue if b missing
    cat "$a" "${a%.a}.b" >"${a%.a}.c"
done

Wildcards and redirections are processed by the shell; cat has no concept of wildcards, nor does it know where you are sending its output.