What is tail?
4 tail examples
Syntax and Options
Related Commands
What is tail?
Tail prints the last N number of lines from given input. By default, it prints last 10 lines of each given file.
4 tail Examples
1. Print the last N lines
To view the last N number of lines from file, just pass the file name with -n option as shown below.
$ tail -n 5 flavours.txt Debian Redhat Gentoo Fedora core
Note: When you simply pass the filename, it prints out the last 10 lines of the file.
2. Print the appended lines as and when the file grows
You can use -f option to output the appended lines of file instantly as shown below,
$ tail -f /var/log/messages
Note: This is very useful to monitor the log files.
3. Terminate the tail command once PID dies
Using –pid with -f option, you can terminate the tail command when the specific process gets over or killed as shown below.
$ tail -f /tmp/debug.log --pid=2575
In the above tail gets terminated immediately when the pid 2575 vanishes.
4. Keep on trying to tail the file even if it is non-existent
Sometimes, the file intended to tail may not be available when you run the tail command and it may get created later or the files becomes inaccessible . By this time, you can use the –retry option to keep on trying to open the file as shown below.
$ tail -f /tmp/debug.log --retry tail: warning: --retry is useful mainly when following by name tail: cannot open `/tmp/log' for reading: No such file or directory
After giving the above warnings, it is trying to open the file.
Syntax and Options
tail [OPTIONS]… [FILE]…
| Short Option | Long Option | Option Description |
|---|---|---|
| -c | –bytes | to print last N bytes from each input file |
| -f | –follow | to print appended data as and when the file grows |
| -n | –lines | to print last N lines from each input file |
| –pid | with -f, to terminate after PID dies | |
| -q | –silent, –quiet | to prevent printing of header information |
| –retry | to keep retrying to open a file even when it is not exist or becomes inaccessible. Useful when it is used with -f | |
| -s | –sleep-interval | to sleep for N seconds between iterations |
| -v | –verbose | to print header information always |