linuxexpert-practice-labs/labs/lpic-1/103-4-streams-pipes-redirects

LPIC-1 103.4: Streams, pipes and redirects

Sending output and errors to files, file names with spaces in pipelines, here-documents, and noclobber.

Before you start

The lab creates /root/streams/, and in /root/streams/spaces/ three files with spaces in their names. Work as root (sudo -i).

Tasks

1. Run ls /etc /nonexistent with the output going to /root/streams/out.txt and the errors to /root/streams/err.txt, then both to /root/streams/both.txt. Try 2>&1 before and after > and compare.
2. Delete the three files in /root/streams/spaces/ with find -print0 | xargs -0. Try plain xargs first on copies and see it fail.
3. Write a here-document into /root/streams/heredoc.txt, and use $(date) inside it, so the file holds the date it was written.
4. Turn on set -o noclobber, try to overwrite a file with >, then use >|. Check it yourself: the first try says "cannot overwrite existing file", the second works.

Hints

• >, 2>, &> or > FILE 2>&1; 2>&1 > FILE sends errors to the terminal, because they go where output went before the redirect.
• cp -r spaces copies, find copies -type f | xargs rm; find spaces -type f -print0 | xargs -0 rm.
• cat > FILE <<EOF ... EOF; with <<'EOF' nothing is expanded.
• set +o noclobber turns it off again.