Does this look good to you?
It shows some regular expression myths that I would like to explode!
Myth 1. If you want to match a specific character, you must put it in square brackets.
WRONG ... Square Brackets are a grouping - if you're looking to match just a single specific character, you can simply add it in without the square brackets. A word of caution
... there are a few characters which need \ protection to make sure they are taken literally outside s, but which have no special significance within the s.
Myth 2. If you want to match something in the middle of a string, you should start and end your regular expression with ".*" - i.e. anything, then (pattern), then anything.
WRONG ... regular expressions match within
a string, so the .* on the beginning and the end are redundant. Two exceptions, however ...
(i) - in Python, the match
method looks at the beginning of a string, so if you're using it to look in the middle of a string, you'll need the .* and
(ii) If you are capturing the string that matches - using capture parenthises for example - a leading .* will select a different
match for you - it'll select the last match in your incoming string rather than the first match.
Myth 3. A "." matches any character at all.
WRONG ... by default, a "." does NOT match a new line character. This only makes a difference if you're matching against a string that may contain multiple lines of text, and this very slight restriction is applied by default so that you can safely match within a single record using .* even if you have multiple records in a long string. "Single line mode" - an s modifier in Perl, and re.DOTALL in Python, allow you to force a dot to truly match on any
character including a new line!
We cover regular expressions on almost all of our courses [Schedule]
. That's Perl, PHP, Python, Tcl, Ruby, ... they're also used and briefly covered on MySQL, Apache httpd (Linux Web Server, and Deploying LAMP), and we have a separate One day regular expression course
too which is suitable for skilled programmers in any of the areas I have mentioned who wish to take their regular expressions further. Regular expression engines are available also in C and Java ... though we only cover them by request during courses on the subjects. Lua's pattern matching is very similar to Regular Expressions (and you can learn a lot from one about the other), but we do not mix the training - if you want to learn about Lua patterns, come on a Lua Course
Illustration - course delegates
. This article was inspired by the gentleman on the left of the picture, who had significant data to comb through and with whom I had long, fascinating and wide ranging discussions on regular expressions. (written 2010-06-13, updated 2010-06-18)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articlesQ806 - Regular Expression Cookbook 
Keeping your regular expressions simple - (2006-04-05) 
Commenting a Perl Regular Expression - (2007-06-12) 
Regular expressions made easy - building from components - (2007-08-16) 
Validating Credit Card Numbers - (2008-10-14) 
Making Regular Expressions easy to read and maintain - (2009-05-10) 
Efficient debugging of regular expressions - (2010-01-04) 
Search and replace in Ruby - Ruby Regular Expressions - (2010-01-31) 
First and last match with Regular Expressions - (2010-04-02) 
Making a Lua program run more than 10 times faster - (2010-04-16) 
Matching a license plate or product code - Regular Expressions - (2011-03-28) 
Getting more than a yes / no answer from a regular expression pattern match - (2012-06-30)Q802 - Object Orientation and General technical topics - Regular Expression Elements 
Commenting Perl regular expressions - (2005-09-30) 
Next course - 7th January 2008, Regular Expressions - (2007-12-21) 
Diagrams to show you how - Tomcat, Java, PHP - (2008-08-22) 
Regular Expressions in PHP - (2008-09-16) 
String matching in Perl with Regular Expressions - (2008-10-20) 
Regular Expressions for the petrified - in Ruby - (2015-06-03) 
Regex Reference sheet - (2017-10-10)
Some other Articles
From home to Nurnberg - journey picturesCanal through Melksham - the options and issuesMacho matching - do not do it!How are you getting on?Regular Expression MythsTravelling across EuropeAfter the Perl course in NurnbergBinary data handling with unpack in PerlThe Merchants AndNuremberg - some pictures