Home Accessibility Courses Twitter The Mouth Facebook Resources Site Map About Us Contact
 
For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Finding text and what surrounds it - contextual grep

grep is a very useful tool for finding all the lines in a file (or series of files) that contain a particular string or match some other pattern / criteria. For example, I have a file that contains data for 52 staff members and I want to find who knows Lua ...

[trainee@melksham Download]$ grep Lua requests.xyz
lisa PHP Python Lua ASP Perl Java
graham Lua Perl Tcl/Tk
[trainee@melksham Download]$


But what if I want to see the context of my matches - to be given back not only the matched lines, but a few lines before and after the match to see what it relates too - "other nearby employees" in my example, but more commonly "the rest of the paragraph / example" in the case of text files. On Linux's grep, you can use the -A and -B options to specify the number of lines to display before and after each match, and the -C option if you want to show the same number before and after. Let's see that:

[trainee@melksham Download]$ grep -A2 -B1 Lua requests.xyz
kerry Perl Tcl/Tk Ruby MySQL
lisa PHP Python Lua ASP Perl Java
margaret XML Perl Ruby MySQL Tcl/Tk
nina Tcl/Tk Perl ASP Ruby
--
fred MySQL Perl Java XML
graham Lua Perl Tcl/Tk
harry PHP Python Java
ivan Ruby Java Perl Tcl/Tk MySQL
[trainee@melksham Download]$ grep -C3 Lua requests.xyz
iris Perl MySQL Java Tcl/Tk
jenny XML Perl Ruby ASP
kerry Perl Tcl/Tk Ruby MySQL
lisa PHP Python Lua ASP Perl Java
margaret XML Perl Ruby MySQL Tcl/Tk
nina Tcl/Tk Perl ASP Ruby
olivia MySQL Python ASP PHP
--
david Perl Tcl/Tk Java
ed Ruby Perl Java PHP
fred MySQL Perl Java XML
graham Lua Perl Tcl/Tk
harry PHP Python Java
ivan Ruby Java Perl Tcl/Tk MySQL
john PHP XML Java Perl
[trainee@melksham Download]$


If you're on a system that's got a version of grep that doesn't support these options, what can you do? Well - you could do worse that write a Perl script - in fact we've used the requirement for a contextual grep for an example on our Perl Programming course.
(written 2009-10-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P208 - Perl - Lists
  [28] Perl for breakfast - (2004-08-25)
  [140] Comparison Chart for Perl programmers - list functions - (2004-12-04)
  [230] Course sizes - beware of marketing statistics - (2005-02-27)
  [240] Conventional restraints removed - (2005-03-09)
  [355] Context in Perl - (2005-06-22)
  [463] Splitting the difference - (2005-10-13)
  [560] The fencepost problem - (2006-01-10)
  [622] Queues and barrel rolls in Perl - (2006-02-24)
  [762] Huge data files - what happened earlier? - (2006-06-15)
  [773] Breaking bread - (2006-06-22)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [968] Perl - a list or a hash? - (2006-12-06)
  [1304] Last elements in a Perl or Python list - (2007-08-16)
  [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
  [1703] Perl ... adding to a list - end, middle, start - (2008-07-09)
  [1828] Perl - map to process every member of a list (array) - (2008-10-09)
  [1917] Out of memory during array extend - Perl - (2008-12-02)
  [1918] Perl Socket Programming Examples - (2008-12-02)
  [2067] Perl - lists do so much more than arrays - (2009-03-05)
  [2226] Revision / Summary of lists - Perl - (2009-06-10)
  [2295] The dog is not in trouble - (2009-07-17)
  [2813] Iterating over a Perl list and changing all items - (2010-06-15)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [2996] Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12)
  [3400] $ is atomic and % and @ are molecular - Perl - (2011-08-20)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3669] Stepping through a list (or an array) in reverse order - (2012-03-23)
  [3870] Writing more maintainable Perl - naming fields from your data records - (2012-09-25)
  [3906] Taking the lead, not the dog, for a walk. - (2012-10-28)
  [3939] Lots of ways of doing the same thing in Perl - list iteration - (2012-12-03)
  [4609] Mapping an array / list without a loop - how to do it in Perl 6 - (2016-01-03)

A166 - Web Application Deployment - Linux Utilities
  [63] Almost like old times - (2004-09-26)
  [71] Comparators in Linux and Unix - (2004-10-03)
  [1361] Korn shell course - (2007-09-22)
  [1366] awk - a powerful data extraction and manipulation tool - (2007-09-25)
  [1690] Conversion of c/r line ends to l/f line ends - (2008-06-28)
  [2145] Using the internet to remotely check for power failure at home (PHP) - (2009-04-29)
  [2320] Helping new arrivals find out about source code examples - (2009-08-03)
  [2638] Finding what has changed - Linux / Unix - (2010-02-17)
  [3446] Awk v Perl - (2011-09-18)
  [3764] Shell, Awk, Perl of Python? - (2012-06-14)
  [3902] Shell - Grep - Sed - Awk - Perl - Python - which to use when? - (2012-10-22)
  [4586] Extending your bash shell with aliases, functions and extra commands - (2015-11-28)
  [4682] One line scripts - Awk, Perl and Ruby - (2016-05-20)


Back to
Clustering on Tomcat
Previous and next
or
Horse's mouth home
Forward to
How do I set up a constant in Python?
Some other Articles
A variable number of arguments in a PHP function
Melksham Forum
Santa Special - Trowbridge and Melksham to Swindon
How do I set up a constant in Python?
Finding text and what surrounds it - contextual grep
Clustering on Tomcat
Load balancing with sticky sessions (httpd / Tomcat)
Sample code with errors in it on our web site
Pantomimes around Melksham - 2009/2010 season
Accidentally typed ci rather than vi?
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page


This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2024: 48 Spa Road • Melksham, Wiltshire • United Kingdom • SN12 7NY
PH: 01144 1225 708225 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/2484_Fin ... -grep.html • PAGE BUILT: Sun Oct 11 16:07:41 2020 • BUILD SYSTEM: JelliaJamb