Piping error messages with grep

Question

I have a script that fails because some files are missing.

Running the script and piping it to grep

$ ./adder | grep Error

produces th

Answer 1

Like piokuc's suggests, combine stderr with stdout. However, I think you are looking a better invocation of grep:

./adder 2>&1 | grep "^Error" | grep -oP '[^ ]*\.root'