问题
I have a script that fails because some files are missing.
Running the script and piping it to grep
$ ./adder | grep Error
produces the following output:
Error in <TFile::ReadBuffer>: error reading all requested bytes from file v2.2_V3_194424_194712/output_853.root, got 0 of 300
Error in <TFile::Init>: v2.2_V3_194424_194712/output_853.root not a ROOT file
and similar output with different files
I'd like to extract the root files like v2.2_V3_194424_194712/output_853.root from this output, but
doing ./adder | grep Error | grep .root doesn't work.
Why is that?
回答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'
回答2:
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
来源：https://stackoverflow.com/questions/12055674/piping-error-messages-with-grep