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

You need to redirect standard error stream (numeric code: 2) from first command in the pipe to standard output stream (numeric code: 1), like this:

$ ./adder 2>&1 | grep Error

Answer 2

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'