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World L1: The Shophouse

Read files: cat, less, head, tail

You will learn: to read a whole file, its first lines, its newest lines, and to watch it grow.

Checked with Linux (Debian 13) on 1 Nov 2026

The problem

The counter keeps an order book, orders.log. It grows all day. You only need the newest orders. What do you do?

Watch

You are hereyou@kedai:~/kedai/counter$

Folder ~/kedai/counter

  • orders.log-rw-r--r--

Services

  • cronrunningstarts at boot
  • sshrunningstarts at boot
  • nginxrunningstarts at boot

cat orders.log prints the whole file at once. Great for short files. A long one flies past your eyes.

Check

Pick the right tool for each job.

Drag a card into a box. Or tap the card, then tap the box.

        Try it

        Show only the last 3 orders: tail -n 3 orders.log.

        You are hereyou@kedai:~/kedai/counter$

        Folder ~/kedai/counter

        • orders.log-rw-r--r--

        Services

        • cronrunningstarts at boot
        • sshrunningstarts at boot
        • nginxrunningstarts at boot

        Predict

        What does head -n 1 orders.log print?

        Try it

        Watch the book grow with tail -f orders.log. It holds the terminal. Stop it with Ctrl+C.

        You are hereyou@kedai:~/kedai/counter$

        Folder ~/kedai/counter

        • orders.log-rw-r--r--

        Services

        • cronrunningstarts at boot
        • sshrunningstarts at boot
        • nginxrunningstarts at boot

        Check

        You opened a long log with less orders.log. You read enough. How do you leave?

        You did it!

        You can now read the top, the end, or a whole file.

        Go deeper (optional)

        In less, Space shows the next page and q quits. /sambal searches, and G jumps to the end. head and tail show 10 lines unless you say -n. cat -n numbers the lines. wc -l counts them.

        Real rep (optional): on Linux, try tail -n 5 /var/log/dpkg.log, then less /etc/os-release and press q.