linuxexpert-practice-labs/labs/linux-plus/1-5-3-text-tools/README.md

Linux+ 1.5.3: Working with text

grep, cut, awk, sed, tr, sort and uniq on real files: users with a login shell, a config file without its comments, an edit with sed, and a word count.

Before you start

The lab clears away the files the tasks create in /tmp, if they're there. Ubuntu empties /tmp at boot, so do the tasks without a reboot. Tasks 1, 2 and 4 ask for findings: write them to the files in /root/lab-answers/ that they name.

Tasks

1. Find the users with a UID from 1000 to 59999 (the regular users) with awk, and write their names, one per line, to /root/lab-answers/1.
2. Strip the comments and blank lines from /etc/ssh/sshd_config, saving what's left to /tmp/sshd.active, and count its lines in the same pipeline. Write the count to /root/lab-answers/2.
3. Copy /etc/ssh/sshd_config to /tmp/s.conf. With sed -i.bak, change the PermitRootLogin line (commented out or not) to PermitRootLogin no, keeping the original as /tmp/s.conf.bak, and compare the two with diff.
4. Find the most common word in the bash man page, and write it to /root/lab-answers/4.

Hints

• awk -F: '$3 >= 1000 && $3 < 60000 {print $1}' /etc/passwd.
• grep -v -E '^\s*(#|$)', tee, wc -l. On the RHEL family only root can read sshd_config: sudo.
• sed -i.bak 's/^#\?PermitRootLogin.*/PermitRootLogin no/'.
• man bash | tr -cs 'A-Za-z' '\n' | tr 'A-Z' 'a-z' | sort | uniq -c | sort -rn | head.