head: First Lines

Some files are huge: hundreds or thousands of lines. Dumping all of that with cat floods your screen. Often you only want a quick peek at the start of a file.

The head command prints just the first lines of a file. By default, the first 10 lines:

head bigfile.log

line 1
line 2
...
line 10

Choosing how many lines: -n

The -n option sets exactly how many lines you want:

head -n 3 bigfile.log

line 1
line 2
line 3

When head is useful

• Checking the header row of a data file
• Seeing how a log file begins
• Sampling a file without scrolling through all of it

Like cat, head only reads. It changes nothing.

Mission: Check and Archive the Boot Sequence

The station's system.log records everything since the last reboot. Engineering wants to verify the boot sequence and keep a copy of the log for the diagnostics folder.

1. Print only the first 5 lines of system.log: the earliest boot events.
2. Create a folder called diagnostics and copy system.log into it as boot.log.
3. Verify the copy by printing just the first 3 lines of diagnostics/boot.log.

Expected result

The first boot events appear, then a shorter 3-line sample of the archived copy. The diagnostics folder holds a faithful copy of the log.