linuxexpert-practice-labs/labs/lpic-1/103-2-text-filters

LPIC-1 103.2: Processing text with filters

Counting with cut, sort and uniq, spotting Windows line endings, splitting and joining files, and following a log.

Before you start

The lab creates /root/filters/ with three text files, report1.txt, report2.txt and report3.txt; one of them has Windows line endings. Work as root (sudo -i), and write answers to the files in /root/lab-answers/. Where the journal is kept only in memory (no /var/log/journal), a reboot loses task 5's message, so check before you reboot.

Tasks

1. Make /root/filters/fruit.txt with the five lines from the chapter:

   apple 3
   banana 12
   cherry 7
   apple 5
   banana 1
   

   Count how many lines mention each fruit with cut, sort and uniq -c, and write the output to /root/lab-answers/1.

2. Count the accounts using each login shell in /etc/passwd, most common first, and write the output to /root/lab-answers/2.

3. Use od -c to find out which of the three report files uses Windows line endings (\r \n), and write its name to /root/lab-answers/3.

4. Split a large file from /var/log into 100-line pieces in /root/filters/split/, join them back with cat into /root/filters/joined.log, and prove the result is identical with sha256sum.

5. Follow /var/log/syslog or /var/log/messages with tail -f in one terminal while running logger hello in another. If neither file exists, your system logs only to the journal: use journalctl -f instead.

Hints

• cut -d' ' -f1 FILE | sort | uniq -c.
• cut -d: -f7, then sort | uniq -c | sort -rn.
• od -c FILE | head; file says "with CRLF line terminators" too.
• split -l 100 FILE /root/filters/split/part-, cat .../part-* > ..., sha256sum. Pick a file that doesn't change while you work, such as cloud-init.log or an older rotated log.
• logger hello; journalctl -f or journalctl -t USER.