Tail (Unix)
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- The correct title of this article is tail (Unix). The initial letter is shown capitalized due to technical restrictions.
tail is a program on Unix and Unix-like systems used to display the last few lines of a text file or piped data. The command-syntax is:
tail [options] <file_name>
By default, tail 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:
tail -n 20 filename
This example shows the last 15 bytes of all files starting with foo:
tail -c 15 foo*
This example shows all lines of filename from the second line onwards:
tail -n +2 filename
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:
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.
[edit] File monitoring
tail has a special command line option -f (follow) that allows a file to be monitored. Instead of displaying the last few lines and exiting, tail displays the lines and then monitors the file. As new lines are added to the file by another process, tail 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:
tail -f /var/adm/messages
To interrupt tail while it is monitoring, break-in with CTRL-C. This command can be run "in the background" with &, see job control.
[edit] See also
[edit] External links
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