`head`: Top of File

head prints the first N lines of a file. The default is 10. It's essential for peeking at a large file without loading everything into the terminal.

Basic usage

head access.log

Shows the first 10 lines.

Specifying a line count

head -n 5 access.log

Shows the first 5 lines. The -n flag sets the number of lines.

You can also use the shorthand:

head -5 access.log

Typical output (log file)

2024-01-15 08:00:01 192.168.1.10 GET /index.html 200
2024-01-15 08:00:03 10.0.0.5 POST /api/login 401
2024-01-15 08:00:07 192.168.1.10 GET /dashboard 200
2024-01-15 08:00:12 10.0.0.8 GET /api/data 200
2024-01-15 08:00:15 192.168.1.10 DELETE /api/user/42 403

Why `head` matters for data work

When you receive an unfamiliar CSV or log file, the first thing to do is:

head -n 5 data.csv

This tells you:

The column names (if there's a header row)
The data format
Whether the file looks right before you process it

Doing this before every pipeline saves you from running a 10-minute job on malformed data.

Using `head` in a pipeline

cat access.log | head -n 3

Same as head -n 3 access.log — but useful when you want to preview the output of another command.

Practice

Show only the first 5 lines of access.log using head -n 5.

Basic usage​

Specifying a line count​

Typical output (log file)​

Why head matters for data work​

Using head in a pipeline​

Practice​