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Making Regular Expressions easy to read and maintain
Have you ever seen a long regular expression made up of so many special characters that you can't read or maintain it very easily? Something like /\(\s*([A-Z]{4})\s+(\d+(?:\.\d*)?)\s*\/\s*(\d+(?:\.\d*)?)\s*\/\s*(\d+(?:\.\d*)?)\s*\)/ We offer a Regular Expression Course that will help you understand things like this more easily ... and also help you write them in what I believe is an easier-to-maintain way: # A 4 letter word in capitals, to be captured $word4c = '\s*([A-Z]{4})\s*'; # White Space $spaces = '\s+'; # A number - may have a decimal point and digits thereafter, to be captured $floatc = '\s*(\d+(?:\.\d*)?)\s*'; !\( $word4c $spaces $floatc / $floatc / $floatc \)!x Although the coding of this example is longer, I have set up a series of intermediate variables that has avoided the need for me to repeat complex patterns. And those same intermediate variables can be used in other matches to similar data, avoid the need for repeated logic. "Why is it when people are so proud of their skill in removing duplicated code by writing functions, they often go and spoil the whole thing by repeating the same regular expression or printf format many many times" I ask myself! (written 2009-05-10) Associated topics are indexed under Q806 - Regular Expression Cookbook[3788] Getting more than a yes / no answer from a regular expression pattern match - (2012-06-30) [3218] Matching a license plate or product code - Regular Expressions - (2011-03-28) [2804] Regular Expression Myths - (2010-06-13) [2727] Making a Lua program run more than 10 times faster - (2010-04-16) [2702] First and last match with Regular Expressions - (2010-04-02) [2608] Search and replace in Ruby - Ruby Regular Expressions - (2010-01-31) [2563] Efficient debugging of regular expressions - (2010-01-04) [1840] Validating Credit Card Numbers - (2008-10-14) [1305] Regular expressions made easy - building from components - (2007-08-16) [1230] Commenting a Perl Regular Expression - (2007-06-12) [672] Keeping your regular expressions simple - (2006-04-05) H107 - String Handling in PHP [4072] Splitting the difference with PHP - (2013-04-27) [4071] Setting up strings in PHP - (2013-04-27) [3790] Solution looking for a problem? Lookahead and Lookbehind - (2012-06-30) [3789] More than just matching with a regular expression in PHP - (2012-06-30) [3534] Learning to program in PHP - Regular Expression and Associative Array examples - (2011-12-01) [3516] Regular Expression modifiers in PHP - summary table - (2011-11-12) [3515] PHP - moving from ereg to preg for regular expressions - (2011-11-11) [3424] Divide 10000 by 17. Do you get 588.235294117647, 588.24 or 588? - Ruby and PHP - (2011-09-08) [3020] Handling (expanding) tabs in PHP - (2010-10-29) [2629] Curly braces within double quoted strings in PHP - (2010-02-09) [2238] Handling nasty characters - Perl, PHP, Python, Tcl, Lua - (2009-06-14) [2046] Finding variations on a surname - (2009-02-17) [1799] Regular Expressions in PHP - (2008-09-16) [1613] Regular expression for 6 digits OR 25 digits - (2008-04-16) [1603] Do not SHOUT and do not whisper - (2008-04-06) [1533] Short and sweet and sticky - PHP form input - (2008-02-06) [1372] A taster PHP expression ... - (2007-09-30) [1336] Ignore case in Regular Expression - (2007-09-08) [1195] Regular Express Primer - (2007-05-20) [1058] PHP Regular expression to extrtact link and text - (2007-01-31) [1008] Date conversion - PHP - (2006-12-26) [728] Looking ahead and behind in a Regular Expression - (2006-05-22) [716] Evaluating arithmetic expressions in configuration files - (2006-05-10) [642] How similar are two words - (2006-03-11) [608] Don't expose your regular expressions - (2006-02-15) [589] Robust PHP user inputs - (2006-02-03) [574] PHP - dividing a string up into pieces - (2006-01-23) [560] The fencepost problem - (2006-01-10) [558] Converting between acres and hectares - (2006-01-08) [493] Running a Perl script within a PHP page - (2005-11-12) [463] Splitting the difference - (2005-10-13) [422] PHP Magic Quotes - (2005-08-22) [337] the array returned by preg_match_all - (2005-06-06) [54] PHP and natural sorting - (2004-09-19) [31] Here documents - (2004-08-28) 55cf
Some other Articles
When should I use OO techniques?In honour of the photograph, I present ... a walk from Reybridge to Lacock Watching the tele Crossrefering documents with uniqueness and inconsistency issues - PHP proof of concept demo Making Regular Expressions easy to read and maintain Updating my public profile - Graham Ellis CATALINA_OPTS v JAVA_OPTS - What is the difference? Admins thoughts on banning a member from a forum Get it right ... if it goes wrong, it takes so much effort to sort out! PHP - getclass v instanceof |
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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 at 50 posts per pageThis 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.
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