How to use tail command in Linux?

Linux tail command displays the last part of one or more files or pipe data (default is 10 lines); can be used to monitor file changes in real time. The following article will introduce to you how to use the Linux tail command. I hope it will be helpful to you.

Linux tail command

The tail command displays the last portion of data from one or more files or pipes (Default is 10 lines); can be used to monitor file changes in real time. One of the most common uses of the tail command is to monitor and analyze logs and other files that change over time, often in conjunction with other tools such as grep.

Basic syntax:

tail [OPTION]... [FILE]...

OPTION: tail option, let’s take a look at some of the most common options.

● -n (--lines) option: Specify the number of lines to be displayed

●-c (--bytes) option: Specify the specific number of bytes to be displayed

● -f (--follow) option: monitor file changes

FILE: Zero or more input file names. If FILE is not specified, or FILE is -, tail reads standard input.

How to use the tail command?

When used in its simplest form without any options, the tail command will display the last 10 lines.

tail filename.txt

How to display a specific number of rows?

You can use the -n (--lines) option to specify the number of lines to display:

tail -n  filename.txt

You can also omit the letter n and just use the hyphen (-) and numbers (without spaces between them).

To display the last 50 lines of a file named filename.txt, you need to use:

tail -n 50 filename.txt

The following example will display the same results as the above command:

tail -50 filename.txt

How to display a specific number of bytes?

You can use the -c (--bytes) option to display a specific number of bytes:

tail -c  filename.txt

For example, to display the last 500 words in the file filename.txt section data, we can use:

tail -c 500 filename.txt

You can also use a multiplier suffix after the number to specify the number of bytes to be displayed. b is multiplied by 512, kB is multiplied by 1000, K is multiplied by 1024, MB is multiplied by 1000000, M is multiplied by 1048576, and so on.

The following command will display the last two kilobytes (2048) of the file filename.txt:

tail -c 2k filename.txt

How do I view a file for changes?

To monitor a file for changes, you need to use the -f (--follow) option:

tail -f filename.txt

The -f option is especially useful for monitoring log files. For example, to display the last 10 lines of the /var/log/nginx/error.log file and monitor the file for updates you want to use:

tail -f /var/log/nginx/error.log

To interrupt the tail command while monitoring the file, press ctrl c.

To continue monitoring the file as it is recreated, you need to use the -f option:

tail -F filename.txt

The -f option is useful when the tail command follows a rotating log file. When used with the -f option, the tail command will reopen the file when it becomes available again.

How to display multiple files

If multiple files are provided as input to the tail command, it will display the last ten of each file OK.

tail filename1.txt filename2.txt

Users have the same options as when displaying a single file.

For example: display the last 20 lines of files filename1.txt and filename2.txt

tail -c 20 filename1.txt filename2.txt

How to use it with other commands?

The tail command can be used in conjunction with other commands. For example, to monitor the Apache access log file and only display the lines containing the IP address 192.168.42.12, you can use:

tail -f /var/log/apache2/access.log | grep 192.168.42.12

Or display the top ten running processes sorted by CPU usage:

ps aux | sort -nk +3 | tail -5

Recommended related video tutorials: "Linux Tutorial"

The above is the content of this article All content, I hope it will be helpful to everyone's study. For more exciting content, you can pay attention to the relevant tutorial columns of the PHP Chinese website! ! !

The above is the detailed content of How to use tail command in Linux?. For more information, please follow other related articles on the PHP Chinese website!