linuxexpert-practice-labs/labs/linux-plus/1-5-2-redirection-and-pipes

Linux+ 1.5.2: Redirection and pipes

Output and errors in separate files, here documents with and without expansion, tee, and file names with spaces through xargs.

Before you start

The lab clears away the files the tasks create, if they're there. Several are in /tmp, which Ubuntu empties at boot, so do the tasks without a reboot and run le-lab check before you clean up.

Tasks

1. Make a directory /tmp/redir and work in it. Run ls /etc /nonexistent four ways: output to out.txt and errors to err.txt; both into all.txt; and with 2>&1 > only-out.txt. Watch where the error goes in the last one.
2. With here documents, write user=$USER to /tmp/a.txt with the variable expanded, and to /tmp/b.txt exactly as written.
3. Count the login shells in /etc/passwd, most common first. Then save getent passwd to /tmp/users.txt and count its lines in the same pipeline.
4. Make a directory /tmp/x with two files, a b.tmp and c d.tmp. See find ... | xargs rm fail on the spaces, then remove them safely with find and xargs. Leave /tmp/x itself.

Hints

• > out.txt 2> err.txt, > all.txt 2>&1; redirections apply left to right.
• << EOF expands variables; << 'EOF' doesn't.
• cut -d: -f7 /etc/passwd | sort | uniq -c | sort -rn; getent passwd | tee /tmp/users.txt | wc -l.
• find /tmp/x -name '*.tmp' -print0 | xargs -0 rm.