head / tail
| Since: | All Linux | |
|---|---|---|
| macOS(2001 Cheetah) | ||
| Bash 1.0(1989) |
The head command displays the beginning of a file, and tail displays the end. In particular, tail -f is commonly used to monitor log files in real time.
Syntax
head [option] [file...] tail [option] [file...]
Options
| Option | Description |
|---|---|
| head file | Displays the first 10 lines of a file. |
| head -n N file | Displays the first N lines. |
| head -c N file | Displays the first N bytes. |
| head -n -N file | Displays all lines except the last N lines. |
| tail file | Displays the last 10 lines of a file. |
| tail -n N file | Displays the last N lines. |
| tail -c N file | Displays the last N bytes. |
| tail -f file | Monitors the end of a file and displays new content in real time as it is appended. |
| tail -F file | Same as -f, but continues tracking even if the file is deleted and recreated. |
| tail -n +N file | Displays lines starting from line N (skips the first N-1 lines). |
Sample Code
The following file is used in the examples below.
~/project/data.csv
id,name,score 1,webmaster,85 2,appserver,72 3,user3,91 4,sysadmin,68 5,devuser,95 6,webmaster,80 7,appserver,88
Display the first 3 lines of the file.
head -n 3 data.csv id,name,score 1,webmaster,85 2,appserver,72
Display the last 3 lines of the file.
tail -n 3 data.csv 5,devuser,95 6,webmaster,80 7,appserver,88
Skip the CSV header (first line) and retrieve all rows from line 2 onward.
tail -n +2 data.csv 1,webmaster,85 2,appserver,72 3,user3,91 4,sysadmin,68 5,devuser,95 6,webmaster,80 7,appserver,88
Check the first 3 lines of /etc/passwd.
head -n 3 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin
Monitor a log file in real time (press Ctrl+C to stop).
tail -f /var/log/nginx/access.log
Continue tracking a log file even after log rotation.
tail -F /var/log/app.log
Combine with a pipe to display only the latest 10 error log entries.
grep "ERROR" app.log | tail -n 10
Common Mistakes
Common Mistake 1: Forgetting -n and getting the wrong number of lines
Without -n, head and tail default to 10 lines. Passing a number without -n is interpreted as a flag on older systems and may cause an error.
head 5 file.txt head: cannot open '5' for reading: No such file or directory
Always use -n to specify the line count explicitly.
head -n 5 file.txt
Common Mistake 2: tail -f does not follow log rotation
tail -f tracks the file descriptor. When a log file is rotated (renamed/replaced), tail -f keeps watching the old file and stops receiving new entries.
tail -f /var/log/app.log （log rotation creates a new file, but tail -f keeps watching the old one）
Use tail -F (capital F) to follow by filename and automatically reopen the file after rotation.
tail -F /var/log/app.log
Notes
tail -f is a command you will use almost daily for server log monitoring. To monitor multiple files at once, you can specify them together: $ tail -f file1 file2. For more powerful log monitoring, tools such as multitail and lnav are also available.
To browse an entire file interactively, use less. See also cat for displaying full file contents.
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