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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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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))
Don't expose your regular expressions

If you're writing an application, it's generally NOT a good idea to take a user input and slap it straight in to a regular expression for matching - quite simply because it's improbable that your user will be familiar with regular expressions and he / she will get all sorts of strange results if she / he puts any special characters into their search string.

Users do often require to enter various search patterns, and I recommend that you come up with a scheme that suits your own type of search; that might involve taking the user's input and using it to indirectly for a regular expression, or it might make for some totally different search.

I was talking about this yesterday to a Perl group, with a user community that's used to using * and ? in file name matching (know as globbing) and who want to do the same on data within Perl. It's a good example where the program shouldn't just pass through the data entered - rather, they should
1. Protect input special characters with a \
2. replace input ? characters with a .
3. replace input * characters with a .*
4. Add ^ and $ anchors

And that will give them the ability to wildcard in the good ole way they wish!
(written 2006-02-15, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P212 - Perl - More on Character Strings
  [453] Commenting Perl regular expressions - (2005-09-30)
  [583] Remember to process blank lines - (2006-01-31)
  [586] Perl Regular Expressions - finding the position and length of the match - (2006-02-02)
  [597] Storing a regular expression in a perl variable - (2006-02-09)
  [737] Coloured text in a terminal from Perl - (2006-05-29)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [1222] Perl, the substitute operator s - (2007-06-08)
  [1230] Commenting a Perl Regular Expression - (2007-06-12)
  [1251] Substitute operator / modifiers in Perl - (2007-06-28)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1510] Handling Binary data (.gif file example) in Perl - (2008-01-17)
  [1727] Equality and looks like tests - Perl - (2008-07-29)
  [1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
  [1947] Perl substitute - the e modifier - (2008-12-16)
  [2230] Running a piece of code is like drinking a pint of beer - (2009-06-11)
  [2379] Making variables persistant, pretending a database is a variable and other Perl tricks - (2009-08-27)
  [2657] Want to do a big batch edit? Nothing beats Perl! - (2010-03-01)
  [2801] Binary data handling with unpack in Perl - (2010-06-10)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)
  [2874] Unpacking a Perl string into a list - (2010-07-16)
  [2877] Further more advanced Perl examples - (2010-07-19)
  [2993] Arrays v Lists - what is the difference, why use one or the other - (2010-10-10)
  [3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
  [3100] Looking ahead and behind in Regular Expressions - double matching - (2010-12-23)
  [3322] How much has Perl (and other languages) changed? - (2011-06-10)
  [3332] DNA to Amino Acid - a sample Perl script - (2011-06-24)
  [3411] Single and double quotes strings in Perl - what is the difference? - (2011-08-30)
  [3546] The difference between dot (a.k.a. full stop, period) and comma in Perl - (2011-12-09)
  [3630] Serialsing and unserialising data for storage and transfer in Perl - (2012-02-28)
  [3650] Possessive Regular Expression Matching - Perl, Objective C and some other languages - (2012-03-12)
  [3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
  [3927] First match or all matches? Perl Regular Expressions - (2012-11-19)
  [4452] Binary data handling - Python and Perl - (2015-03-09)

H107 - String Handling in PHP
  [31] Here documents - (2004-08-28)
  [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)
  [642] How similar are two words - (2006-03-11)
  [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)
  [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)
  [2165] Making Regular Expressions easy to read and maintain - (2009-05-10)
  [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)
  [3788] Getting more than a yes / no answer from a regular expression pattern match - (2012-06-30)
  [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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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.

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