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 as below, or enter http://melksh.am/nnnn for individual articles
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[1230] Commenting a Perl Regular Expression - (2007-06-12)
[1305] Regular expressions made easy - building from components - (2007-08-16)
[1840] Validating Credit Card Numbers - (2008-10-14)
[2563] Efficient debugging of regular expressions - (2010-01-04)
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[2702] First and last match with Regular Expressions - (2010-04-02)
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[2804] Regular Expression Myths - (2010-06-13)
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[54] PHP and natural sorting - (2004-09-19)
[337] the array returned by preg_match_all - (2005-06-06)
[422] PHP Magic Quotes - (2005-08-22)
[463] Splitting the difference - (2005-10-13)
[493] Running a Perl script within a PHP page - (2005-11-12)
[558] Converting between acres and hectares - (2006-01-08)
[560] The fencepost problem - (2006-01-10)
[574] PHP - dividing a string up into pieces - (2006-01-23)
[589] Robust PHP user inputs - (2006-02-03)
[608] Don't expose your regular expressions - (2006-02-15)
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[716] Evaluating arithmetic expressions in configuration files - (2006-05-10)
[728] Looking ahead and behind in a Regular Expression - (2006-05-22)
[1008] Date conversion - PHP - (2006-12-26)
[1058] PHP Regular expression to extrtact link and text - (2007-01-31)
[1195] Regular Express Primer - (2007-05-20)
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[1372] A taster PHP expression ... - (2007-09-30)
[1533] Short and sweet and sticky - PHP form input - (2008-02-06)
[1603] Do not SHOUT and do not whisper - (2008-04-06)
[1613] Regular expression for 6 digits OR 25 digits - (2008-04-16)
[1799] Regular Expressions in PHP - (2008-09-16)
[2046] Finding variations on a surname - (2009-02-17)
[2238] Handling nasty characters - Perl, PHP, Python, Tcl, Lua - (2009-06-14)
[2629] Curly braces within double quoted strings in PHP - (2010-02-09)
[3020] Handling (expanding) tabs in PHP - (2010-10-29)
[3424] Divide 10000 by 17. Do you get 588.235294117647, 588.24 or 588? - Ruby and PHP - (2011-09-08)
[3515] PHP - moving from ereg to preg for regular expressions - (2011-11-11)
[3516] Regular Expression modifiers in PHP - summary table - (2011-11-12)
[3534] Learning to program in PHP - Regular Expression and Associative Array examples - (2011-12-01)
[3789] More than just matching with a regular expression in PHP - (2012-06-30)
[3790] Solution looking for a problem? Lookahead and Lookbehind - (2012-06-30)
[4071] Setting up strings in PHP - (2013-04-27)
[4072] Splitting the difference with PHP - (2013-04-27)
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