Cheatsheet & Examples: tail
The tail command is used to display the last part of a file, typically the last 10 lines by default. It is commonly used for monitoring log files or reviewing the end of large text files.
Display the last 10 lines of a file
Example Usage:tail filename.txt
What it does:
Outputs the final 10 lines of the specified file.
Command-line Arguments Explained:
filename.txt: The file to analyze.tailreads from this file and displays the last 10 lines.
Display a specified number of lines from the end of a file
Example Usage:tail -n 20 filename.txt
What it does:
Prints the last 20 lines of the file.
Command-line Arguments Explained:
-n: An option to specify the number of lines to display (as a parameter).20: The number of lines to output from the end of the file.filename.txt: The file to analyze.
Follow a file in real time as it grows
Example Usage:tail -f filename.log
What it does:
Continuously outputs new lines appended to the file, useful for monitoring log files.
Command-line Arguments Explained:
-f: An option to "follow" the file, keeping it open and displaying updates.filename.log: The file to monitor for real-time changes.
Display lines starting from a specific line number
Example Usage:tail -n +50 filename.txt
What it does:
Shows lines from the 50th line onward in the file.
Command-line Arguments Explained:
-n: An option to define the number of lines.+50: A parameter to start from line 50 (inclusive) instead of the end.filename.txt: The file to process.
Display the last N bytes of a file
Example Usage:tail -c 100 filename.txt
What it does:
Outputs the last 100 bytes of the file, useful for small sections of large files.
Command-line Arguments Explained:
-c: An option to specify the number of bytes to display (as a parameter).100: The byte count to retrieve from the end of the file.filename.txt: The target file.
Reverse the file's output line by line
Example Usage:tail -r filename.txt
What it does:
Prints the file's content in reverse order, starting from the last line.
Command-line Arguments Explained:
-r: An option to reverse the output of the file.filename.txt: The file to process in reverse.
Suppress headers when multiple files are processed
Example Usage:tail -q filename1.txt filename2.txt
What it does:
Displays the last 10 lines of each file without headers, even for multiple files.
Command-line Arguments Explained:
-q: An option to suppress the "filename" headers for multiple files.filename1.txt: First file to analyze.filename2.txt: Second file to analyze.
Show headers when processing a single file
Example Usage:tail -v filename.txt
What it does:
Displays the last 10 lines of the file and includes the "filename" header.
Command-line Arguments Explained:
-v: An option to show headers for the file, even when only one is used.filename.txt: The file to analyze.
Wait for a specific process ID (PID) to terminate
Example Usage:tail --pid=1234 filename.txt
What it does:
Waits until the specified PID stops before displaying the file's output.
Command-line Arguments Explained:
--pid=1234: An option to track the process ID and pause until it exits.filename.txt: The file to read after the PID terminates.
Retry opening a file if it is temporarily inaccessible
Example Usage:tail --retry filename.txt
What it does:
Attempts toreopen the file if it is removed and recreated, avoiding errors.
Command-line Arguments Explained:
--retry: An option to keep trying to open the file if it is not accessible initially.filename.txt: The file to monitor.
Suppress error messages for non-existent files
Example Usage:tail --silent filename.txt
What it does:
Avoids displaying error messages when attempting to read a missing file.
Command-line Arguments Explained:
--silent: An alias for-q, suppressing headers and errors for multiple files.filename.txt: The file to process.
Display help information
Example Usage:tail --help
What it does:
Prints a usage summary and available options for tail.
Command-line Arguments Explained:
--help: A flag to show help documentation.
Display version information
Example Usage:tail --version
What it does:
Outputs the version of the tail utility installed on the system.
Command-line Arguments Explained:
--version: A flag to show the program's version.
