Tail (Unix)
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'''tail''' is a [[Computer program|program]] on [[Unix]] and [[Unix-like]] systems used to display the last few lines of a text [[Computer file|file]] or [[pipe (computing)|pipe]]d data.
==Syntax==
The command-[[syntax]] is:
<tt>tail [options] <file_name></tt>
By default, <tt>tail</tt> will print the last 10 lines of its input to the [[standard output]]. With [[command line]] options the number of lines printed and the printing units (lines, blocks or bytes) may be changed. The following example shows the last 20 lines of ''filename'':
<tt>tail -n 20 ''filename''</tt>
This example shows the last 15 bytes of all files starting with ''foo'':
<tt>tail -c 15 ''foo*''</tt>
This example shows all lines of ''filename'' from the second line onwards:
<tt>tail -n +2 ''filename''</tt>
Using an older syntax (still used in 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:
<tt>tail -20 ''filename''</tt>
<tt>tail -50c ''filename''</tt>
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.
==File monitoring==
<tt>tail</tt> has a special command line option <tt>-f</tt> (follow) that allows a file to be monitored. Instead of displaying the last few lines and exiting, <tt>tail</tt> displays the lines and then monitors the file. As new lines are added to the file by another [[Process (computing)|process]], <tt>tail</tt> updates the display. This is particularly useful for monitoring log files. 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'':
<tt>tail -f /var/adm/messages</tt>
To interrupt <tt>tail</tt> while it is monitoring, break-in with CTRL-C. This command can be run "in the background" with <tt>&</TT>, see [[job control (Unix)|job control]].
==Variants==
* [http://freshmeat.net/redir/ccze/33590/url_homepage/ccze.html CCZE] is tail-like while displaying its output in color
* [http://sourceforge.net/projects/pctail/ pctail] Like CCZE: Python Colorized TAIL, a colorized tail made in python which tails and colorizes syslog output.
* [http://www.goof.com/pcg/marc/root-tail.html root-tail] displays the output in the [[X-server]] root window
* [http://distanz.ch/inotail/ Inotail]: the regular tail polls every second to see if new data can be displayed. Inotail uses the [[Linux]] [[kernel (computer science)|kernel]]'s [[inotify]]-interface so that it only checks for new data when there really is some.
* [http://www.vanheusden.com/multitail/ MultiTail] not only displays logfiles in colors, it can also merge, filter, scrollback and split a terminal window in subwindows. It is more or less a combination of tail, [[sed]], [[watch]], CCZE/pctail, [[grep]], [[diff]], [http://cosoleto.free.fr/beeper/ Beeper] and others.
==See also==
*[[head (Unix)|head]]
*[[List of Unix programs]]
{{Unix commands}}
== External links ==
* [http://www.gnu.org/software/coreutils/manual/html_node/tail-invocation.html GNU Project documentation for tail]
* [http://www.freebsd.org/cgi/man.cgi?query=tail&apropos=0&sektion=0&manpath=FreeBSD+5.3-RELEASE+and+Ports&format=html FreeBSD documentation for tail]
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