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
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|