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.

Solution 1

for dir in */folder_*/*; do 
  [[ -d "$dir" ]] && ( cd "$dir" && cat file.a file.b > file.c )
done

I run the cd && cat in a subshell so you don't have to cd back to where you started.

Solution 2

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

Solution 3

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.

Comments

[Admin]

So the only alternative I can come up with is to loop through all the directories and subdirectories by ls, build up and save the entire path then execute the cat command for each file instance. Oh well... anyway thx.

[SourceSeeker]

@lorendarith: Don't loop with ls - use globbing for f in *