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tail is a
program Program, programme, programmer, or programming may refer to: Business and management * Program management, the process of managing several related projects * Time management * Program, a part of planning Arts and entertainment Audio * Progra ...
available on
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
,
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
systems,
FreeDOS FreeDOS (formerly Free-DOS and PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running Legacy system, legacy software and supporting embedded system ...
and
MSX-DOS MSX-DOS is a discontinued disk operating system developed by Microsoft for the 8-bit home computer standard MSX, and is a cross between MS-DOS 1.25 and CP/M-80 2. MSX-DOS MSX-DOS and the extended BASIC with 3½-inch floppy disk support ...
used to display the tail end of a text
file File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...
or
pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circular ...
d data.


Implementations

The version of tail bundled in
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
coreutils The GNU Core Utilities or coreutils is a package of GNU software containing implementations for many of the basic tools, such as cat, ls, and rm, which are used on Unix-like operating systems. In September 2002, the ''GNU coreutils'' were cr ...
was written by Paul Rubin, David MacKenzie, Ian Lance Taylor, and Jim Meyering. The command is available as a separate package for
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
as part of the
UnxUtils UnxUtils is a collection of ports of common GNU Unix-like utilities to native Win32, with executables only depending on the Microsoft C- runtime msvcrt.dll. The collection was last updated externally on April 15, 2003, by Karl M. Syring. The mo ...
collection of
native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...
Win32 The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces (APIs) available in the Microsoft Windows operating systems. The name Windows API collectively refers to several different platform implementations th ...
ports A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...
of common GNU Unix-like utilities. The
FreeDOS FreeDOS (formerly Free-DOS and PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running Legacy system, legacy software and supporting embedded system ...
version was developed by M. Aitchison. A tail command is also part of
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
's ''MSX-DOS2 Tools'' for
MSX-DOS MSX-DOS is a discontinued disk operating system developed by Microsoft for the 8-bit home computer standard MSX, and is a cross between MS-DOS 1.25 and CP/M-80 2. MSX-DOS MSX-DOS and the extended BASIC with 3½-inch floppy disk support ...
version 2. ''CCZE'' is tail-like while displaying its output in color. ''pctail'' is similar to CCZE. It is a colorized tail programmed in
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
which tails and colorizes syslog output. ''Inotail'' is a deprecated implementation of
inotify inotify ( inode notify) is a Linux kernel subsystem created by John McCutchan, which monitors changes to the filesystem, and reports those changes to applications. It can be used to automatically update directory views, reload configuration files ...
kernel interface. The early implementation of tail polled every second to see if new data can be displayed, as tail implemented inotifiy kernel interface Inotail become deprecated and it is not longer maintained. Inotail used the
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...
's
inotify inotify ( inode notify) is a Linux kernel subsystem created by John McCutchan, which monitors changes to the filesystem, and reports those changes to applications. It can be used to automatically update directory views, reload configuration files ...
-interface introduced in version 2.6.13 in August 2005 so that it only checks for new data when there really is some. MultiTail not only displays logfiles in colors, it can also merge, filter, scrollback and split a terminal window into subwindows. It is more or less a combination of tail,
sed sed ("stream editor") is a Unix utility that parses and transforms text, using a simple, compact programming language. It was developed from 1973 to 1974 by Lee E. McMahon of Bell Labs, and is available today for most operating systems. sed w ...
,
watch A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached by ...
, CCZE/pctail,
grep grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the sam ...
,
diff In computing, the utility diff is a data comparison tool that computes and displays the differences between the contents of files. Unlike edit distance notions used for other purposes, diff is line-oriented rather than character-oriented, but it ...
, Beeper and others.


Syntax

The command-
syntax In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituency) ...
is: tail ptions By default, will output the last 10 lines of its input to the
standard output In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
. With
command line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
options, the amount of output and the units (lines, blocks or bytes) may be changed. In the following example only the last line of the reports is output: $ tail -n1 report-13*


> report-1301 <

Total tons output for month of January '13 was 523


> report-1302 <

Total tons output for month of February '13 was 272


> report-1303 <

Total tons output for month of March '13 was 623
This example outputs the last 4 characters of the reports, silently suppressing the filenames. Notice that the count includes the newline character at the end of each line and so the output does not include a leading space one might expect. $ tail --silent -c4 report* 523 272 623 This example shows all lines of report from the second line onwards: tail -n +2 report Using an older syntax (still used in older version of Sun Solaris as the -n option is not supported), the last 20 lines and the last 50 bytes of ''filename'' can be shown with the following command: tail -20 ''filename'' tail -50c ''filename'' However this syntax is now obsolete and does not conform with the POSIX 1003.1-2001 standard. Even if still supported in current versions, when used with other options (like -f, see below), these switches could not work at all. As with all Unix commands, use
man pages A man page (short for manual page) is a form of software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and ev ...
on the running system for specific options and actions.


File monitoring

has two special command line option and (follow) that allows a file to be monitored. Instead of just displaying the last few lines and exiting, displays the lines and then monitors the file. As new lines are added to the file by another
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...
, updates the display. This is particularly useful for monitoring log files. Ancient versions of tail poll the file every second by default but tail from the
GNU coreutils The GNU Core Utilities or coreutils is a package of GNU software containing implementations for many of the basic tools, such as cat, ls, and rm, which are used on Unix-like operating systems. In September 2002, the ''GNU coreutils'' were cr ...
as of version 7.5 support the
inotify inotify ( inode notify) is a Linux kernel subsystem created by John McCutchan, which monitors changes to the filesystem, and reports those changes to applications. It can be used to automatically update directory views, reload configuration files ...
infrastructure introduced in Linux kernel version 2.6.13 in August 2005 which only check the file when is notified of changes by the kernel. The following command will display the last 10 lines of ''messages'' and append new lines to the display as new lines are added to ''messages'': tail -f /var/adm/messages To keep following the log even when it is recreated, renamed, or removed as part of log rotation, at least BSD and GNU implementations provide a option which is useful in cases when the user is following a log file that rotates. tail -F /var/adm/messages To interrupt while it is monitoring, break-in with Ctrl+C. This command can be run "in the background" with , see job control. If the user has a command's result to monitor, the
watch A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached by ...
command can be used. There is a
GNU Emacs GNU Emacs is a free software text editor. It was created by GNU Project founder Richard Stallman, based on the Emacs editor developed for Unix operating systems. GNU Emacs has been a central component of the GNU project and a flagship project of ...
mode that emulates the functionality of , called .


See also

*
head (Unix) head is a program on Unix and Unix-like operating systems used to display the beginning of a text file or piped data. Syntax The command syntax is: head ptions<file_name> By default, head will print the first 10 lines of its input t ...
*
less (Unix) less is a terminal pager Computer program, program on Unix, Microsoft Windows, Windows, and Unix-like systems used to view (but not change) the contents of a text file one screen at a time. It is similar to , but has the extended capability of al ...
*
List of Unix commands This is a list of Unix commands as specified by IEEE Std 1003.1-2008, which is part of the Single UNIX Specification (SUS). These commands can be found on Unix operating systems and most Unix-like operating systems. List See also * List of G ...


References


External links


GNU Project documentation for tail
* * {{Core Utilities commands Unix SUS2008 utilities Unix text processing utilities Plan 9 commands Inferno (operating system) commands IBM i Qshell commands