Using the tail Command
The tail command is used to display the last part of files.
It's particularly useful for viewing the end of log files or any file that is being updated in real-time.
Syntax
The basic syntax of the tail command is:
tail [OPTION]... [FILE]...Example
tail logfile.txt
line 91
line 92
line 93
line 94
line 95
line 96
line 97
line 98
line 99
line 100Options
The tail command has several options to customize its behavior:
- -n [number] : Display the last [number] lines of the file.
- -f : Follow the file as it grows, useful for monitoring log files.
- -c [number] : Display the last [number] bytes of the file.
- --pid=[pid] : Terminate after the process with the given PID dies.
- --retry : Keep trying to open a file even if it is inaccessible.
Option: -n [number]
The -n option allows you to specify the number of lines to display from the end of the file.
By default, tail shows the last 10 lines.
Example: Display Last 5 Lines
tail -n 5 logfile.txt
line 96
line 97
line 98
line 99
line 100Option: -f
The -f option is used to follow a file as it grows, which is particularly useful for monitoring log files in real-time.
Example: Follow Log File
tail -f logfile.txt
line 91
line 92
line 93
line 94
line 95
line 96
line 97
line 98
line 99
line 100
line 101Option: -c [number]
The -c option allows you to display the last [number] bytes of a file instead of lines.
Example: Display Last 20 Bytes
tail -c 20 logfile.txt
end of logfile.txtOption: --pid=[pid]
The --pid option terminates tailing after the process with the given PID dies. This is useful for stopping the tail operation when a related process ends.
Example: Terminate After Process Ends
tail -f --pid=1234 logfile.txt
line 91
line 92
line 93
...Option: --retry
The --retry option makes tail keep trying to open a file even if it is inaccessible. This is useful for files that may be temporarily unavailable.
Example: Retry Opening File
tail --retry -f logfile.txt
tail: cannot open 'logfile.txt' for reading: No such file or directory
line 91
line 92
line 93
...Use Cases
Common scenarios where the tail command is beneficial include:
- Monitoring server logs to detect issues in real-time.
- Checking the latest entries in a continuously updated file.
- Debugging applications by reviewing recent log entries.