Satisfy Your Technical Curiosity Regular Expressions Roy Osherove Methodology & Team System Expert Sela Group The

Satisfy Your Technical Curiosity

Regular Expressions

Roy Osherovewww.iserializable.com

Methodology &

Team System Expert

Sela Group

www.Sela.co.il

The hidden power language


Tools

http://tools.osherove.comwww.ISerializable.com


The Log File


Developer Problem– Make this log file useful

Old log file from a *nix system’s entriesConverted to and from various formatsSearched by usersFormat may change Search fields can be added, removed or renamed at runtime

Date CPUs|ram|cpu HH:mm:ss action user domain.machine25/05/1998 1|00512|x86 21:49:12 [Search] Anakin Antler.Anita125/05/98 1|00512|x86 21:51:15 [Update] Anakin Antler.Anita126/05/1998 1|00256|x86 11:02:45 [Search] Darth Cydot.Uk.Gerry2k26/05/98 1|00256|x86 11:12:49 [Update] Darth Cydot.Uk.Gerry2k27/05/98 1|00512|x86 15:34:30 [Search] Anakin Anterl.Anita112/08/1998 2|01024|x86 10:14:53 [Search] Obi Monaco.Huarez


About 15 minutes later…

Done.

About 45 minutes later…Home early.


You can be home early too!Regex is easier than you think


What are Regular Expressions?A language to describe a language using “patterns”Think SQL or XPath – for textOriginated with Perl and *nix shell scriptingMany variations and frameworks exist. Only one for .NET (for now)Used in most languages


Common Regex Uses

Text ValidationPhones, emails, address or any format requirement

Text ManipulationTransform text

Text ParsingFind in files, site Scraping, data collection


What .NET brings to the plate

Full object modelExtended syntaxOptimization techniques in the framework


.NET Regular ExpressionsShow up in several places:

In the classes of the System.Text.RegularExpressions namespace

Via the RegularExpressionValidator validator control (for ASP.NET)Sprinkled in dozens of other places

Browser capabilities filterIn the WSDL <match> tagAnd many more


Key Classes within System.Text.RegularExpressions

RegexContains the pattern and matching optionsImportant methods:

IsMatch() returns booleanReplace() returns a stringSplit() returns a string array…

Main Use: Validation, Splitting, Replacing text


The Process

Pattern

Input

Regex

Matches

Splits

TextReplace text

Options


Validation


Syntax

Match exact text as written in the pattern‘a’ will match all ‘a’ in the text.

Except for special symbols:


Enclosing Alternatives with []The square brackets allow you to specify a list of alternate values. Used in conjunction with the – operator, you can even specify character ranges.

[Cc] Capital or lowercase c[A-Z] Any capital letter A through Z[A-Za-z] Any capital or lowercase letter[0-9] Any digit 0 through 9[A-Za-z0-9] Any letter or digit[0-9.+-&=%] Any digit or special char listed

Notice: no escape needed


Controlling ExpressionFrequency with {}

The {} operators allow you to control the frequency of the preceding expression. The expression takes one of these two forms:

{occurrences} [A-Za-z]{3}

{MinOccurrences, MaxOccurences} [A-Za-z]{1,3}


Basic Frequency Operators? 0 or 1* 0 or more+ 1 or moreSo,

3+ Will match

3, 33, 3333but not

45, 678.


Wildcard Operator: .. matches any non-newline character

Unless multiline mode has been turned on for the patternExamples:

A.$ would match a capital A followed by one any character.

Will not match Abc

A.+ would match a capital A followed by one or more non-newline characters\.htm.? would match ".htm" followed by

an optional non-newline characterBackslash == escape characters that have reserved meanings in regular expressions


Convenience Expressions\d

Any digit

\DAny non-digitMust match something else one

\sAny whitespace character (such as a space or tab)

\SAny character other than a whitespace character

\wAny number or letter

\WAny character other than a number or letter

Many more: Unicode, Hex Values, negative lookups…


Quick Quiz!

[A-Za-z]{3}3 capital or lowercase lettersAbc, abc, aBC,1bc

[A-Z][a-z]{2,4}A capital letter followed by at least 2 but not more than 4 lowercase lettersAbc, Acbde, abcde, ABcde

\w{3,8}\.\w{3}3 to 8 AlphaNumeric characters, followed by a dot and 3 alpha numericsFilename.txt, d0main.com, 1234.567, 34.456


Splitting and Manipulating


The Spammer


(2) Key Classes within System.Text.RegularExpressions

MatchCollection - MatchMatchCollection stores all the matches found

GroupCollection - GroupCaptureCollection - Capture

Regex.Match() returns MatchRegex.Matches() returns MatchCollection…

Main Use: Parsing, searching, collecting data


Simple parsingParsing for emails


Grouping(the coolest part)


Grouping (pay attention!)Groups give us object models

HTML [email protected]

Create a capture hierarchy and use it in code

[\w\.\-]+@ [\w\.\-]+\.\w{2,5}

(?<userName>[\w\.\-]+)@(?<domain>[\w\.\-]+\.\w{2,5})


Grouping Emails& The Regulator


Regulazy

Build simple expressions by exampleNo syntax knowledge neededFreeTools.osherove.com


When not to use Regex

When its easier and more readable to do it otherwiseNot just because it’s “cool”Hard to readSteep learning curveHard to maintain

“Sometimes, when confronted with a problem, you might decide to solve it with Regular Expressions for the wrong reasons. Now you you’ve got two problems.”


Summary

Amazing parsing flexibilityGood skill to have anywhereCan save you time and nervesWith Power comes responsibilityWeigh the pros and cons before using


Resources

The Regulator tools.osherove.comRegulazy tools.osherove.comRegexlib.com – Regex archive (http://www.regexlib.com) + Cheat Sheethttp://www.regular-expressions.info

Roy Osherove: [email protected]: www.iserializable.com


Thank you!

Questions?

Roy Osherove: [email protected]: www.iserializable.com


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Satisfy Your Technical Curiosity Regular Expressions Roy Osherove Methodology & Team System Expert Sela Group The