|May the source be with you, but remember the KISS principle ;-)|
|Contents||Bulletin||Scripting in shell and Perl||Network troubleshooting||History||Humor|
|News||Unix Utilities||Recommended Links||Tail||Syntax||Reference||Pipes|
|tac command||Syslog viewers||Syslog analyzers||Log Colorizing||uniq||tr||Logwatch|
|Perl re-implemenations||Syslog tips||sort||Perl One-Liners||AWK||Humor||Etc|
The external head command displays the first few lines of a file. It displays however many lines you specify as an option. If you do not specify the number of lines to display, head defaults to ten. Its cousin is the tail command.
head [ -n ] filehere n is the number of lines to display starting from the beginning of each file. GNU head is much more capable than many people (even seasoned sysadmins) think.
By default, head prints the fist 10 lines. You can specify a specific number of lines with the --lines=n (or -n n) switch.
$ head -n 50 /var/log/messages
You can abbreviate the -n switch to a minus sign and the number of lines.
$ head -50 /var/log/messages
Combining tail and head in a pipeline, you can display any line or range of lines in the file:
$ head -5000 /var/log/messages | tail -100
If the starting line is a plus sign instead of a minus sign, tail counts that number of lines from the start of the file and prints the remainder. This is a feature of tail, not the head command.
$ tail +1700 /var/log/messages
When using head or tail on arbitrary files in a script, always check to make sure that the file is a regular file to avoid unpleasant surprises.
The head command and, especially, tail command are often used in Web log analysts based on pipes.
The head command is useful for verifying what type of data is in a file. It can be used to view the first few lines of an ASCII file to visually decide what data is contained in the file. You might consider head as a special version of the cat command, allowing you to view the beginning portion of the file.
If more than one file is specified on the command line, head precedes each file with a line like:
===> filename <===
If only one file is given on the command line, head does not inform you of the filename being displayed
If you want the name of the file displayed despite the fact that its the only one you can use /dev/null as the second file or the first file
head -10 file /dev/null
You may choose to use head to display the entire contents of multiple short files so each file will be preceded by its filename. In this case you need to specify n large enough. The following command provides an example:
head -99999 file1 file2 file3
Unix Tools for Web log Analysis
% sort -t" " -k 3 a.txt | head -1
TTTT head and tail
Sometimes you don't want to look at a whole file or all the output from a command, but just the first or last few lines of it.
head and tail provide a means to this end. Unfortunately, they seem to have been written by different people with different ideas about what would be useful, so they work a little differently.
headhead is used to show the first few lines of a file or stream. By default it shows 10 lines:
% ypcat passwd | head bsmith:*:1243:317:Bob Smith:/home/baker-a/bsmith:/bin/csh wayne:*:182:60:Wayne Simpson:/home/wayne:/bin/csh walker:*:1791:100:Lisa Walker:/home/dogbert-a/walker:/bin/csh jim:*:1644:100:Jim Smith:/home/dogbert-a/jim:/bin/csh paul:*:1724:135:Paul Jones:/home/dilbert-a/paul:/bin/csh harry:*:1611:100:Harry Palmer:/home/pkduck-f/harry:/bin/csh alex:*:1959:100:Alex Watson:/home/alex:/bin/csh sue:*:1988:100:Sue Foo:/home/sue:/bin/csh marty:*:1318:78:Marty Taylor:/home/manfac-a/home/marty:/bin/csh
You can specify a different number of lines by prefacing the number with a hyphen ("-"):
% ypcat passwd | head -2 bsmith:*:1243:317:Bob Smith:/home/baker-a/bsmith:/bin/csh wayne:*:182:60:Wayne Simpson:/home/wayne:/bin/csh
If you specify more than one filename on the commandline, head will show the first few lines of each file with a one-line banner identifying each file:
% head -2 /usr/man/man1/head.1 /usr/man/man1/tail.1 ==> /usr/man/man1/head.1 <== .\" @(#)head.1 1.17 90/02/15 SMI; from UCB 4.1 .TH HEAD 1 "9 September 1987" ==> /usr/man/man1/tail.1 <== .\" @(#)tail.1 1.14 90/02/15 SMI; from S5R2 6.2 83/09/02 .TH TAIL 1 "14 August 1989"
Softpanorama hot topic of the month
Unix head command
head (Unix) - Wikipedia, the free encyclopedia
TTTT head and tail
FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit exclusivly for research and educational purposes. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner.
ABUSE: IPs or network segments from which we detect a stream of probes might be blocked for no less then 90 days. Multiple types of probes increase this period.
Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers : Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism : The Iron Law of Oligarchy : Libertarian Philosophy
War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda : SE quotes : Language Design and Programming Quotes : Random IT-related quotes : Somerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose Bierce : Bernard Shaw : Mark Twain Quotes
Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 : Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law
Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds : Larry Wall : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOS : Programming Languages History : PL/1 : Simula 67 : C : History of GCC development : Scripting Languages : Perl history : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history
The Peter Principle : Parkinson Law : 1984 : The Mythical Man-Month : How to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite
Most popular humor pages:
Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor
The Last but not Least
Copyright © 1996-2016 by Dr. Nikolai Bezroukov. www.softpanorama.org was created as a service to the UN Sustainable Development Networking Programme (SDNP) in the author free time. This document is an industrial compilation designed and created exclusively for educational use and is distributed under the Softpanorama Content License.
Original materials copyright belong to respective owners. Quotes are made for educational purposes only in compliance with the fair use doctrine.
FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available to advance understanding of computer science, IT technology, economic, scientific, and social issues. We believe this constitutes a 'fair use' of any such copyrighted material as provided by section 107 of the US Copyright Law according to which such material can be distributed without profit exclusively for research and educational purposes.
This is a Spartan WHYFF (We Help You For Free) site written by people for whom English is not a native language. Grammar and spelling errors should be expected. The site contain some broken links as it develops like a living tree...
|You can use PayPal to make a contribution, supporting development of this site and speed up access. In case softpanorama.org is down you can use the at softpanorama.info|
The statements, views and opinions presented on this web page are those of the author (or referenced source) and are not endorsed by, nor do they necessarily reflect, the opinions of the author present and former employers, SDNP or any other organization the author may be associated with. We do not warrant the correctness of the information provided or its fitness for any purpose.
Last modified: September 28, 2017