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The OmniFoundation Kit contains several classes, two of which are used to perform regular expression searching. OFRegularExpression and OFRegularExpressionMatch are contained in the General Classes folder in the OmniFoundation project.

This is not an introduction into regular expressions, please try “man perlre” in your terminal or look up for some more info on regular expressions in general. As there is no documentation for the OmniFramework I cannot tell you what actual differences there are between eg. the Perl, the Python or the OF implmentation of regular expressions

The use of the two classes to scan strings for regular expressions is fairly straightforward. You start of by allocating a OFRegularExpression with a regular expression string.

regexObj = [[OFRegularExpression alloc] initWithString:regexString];

When composing the regexString one has to be careful with the character ‘' in regular expressions, as it is also a meta character in NSString. Thus the ‘' becomes ‘\’. If you want to match ’, which is a meta character in regular expressions, you must escape it with ‘' in the regular expression finally making the match string ‘\. If you want to match ‘', it has to be escaped in the regular expression and in the NSString so the match string for that is ‘\\’.

There is an optional parameter to the initWithString: method isGreedy: it is set to YES by default. This means the regular Expression will always return the longest match it can find. If it is set to NO the match will be return as soon as the regular expression is satisfied.

regexObj is usable, as long as the regular Expression that is being look for is not changed this object can be reused many times.

If you just need to know if there is a match in the string then you can get through with just using the hasMatchInString: method of the regexObj.

if ([regexObj hasMatchInString:searchString]) { … }

if you need to know what the string was that was the actual match or if there could be more matches within that string you will need to use an instance of OFRegularExpressionMatch that is returned by OFRegularExpression. The matchObj is also used to get further matches in the string. For example here is a little fragment that prints out all the WordsJammedTogether within a string


nextMatch returns nil if there are no more matches. Regular expressions can contain groups called subexpressions; these are accessed via the subexpressionAtIndex method.

For reference here are the public interfaces to the two classes, without the variable declarations.

@interface OFRegularExpression : OFObject


@interface OFRegularExpressionMatch : OFObject


– HaRald (slight cleanup by AaronZinman)

Questions, Comments And Suggestions:

See also AGRegex and MOKit at ObjectLibrary for alternatives to OmniFoundation (which is a bit heavyweight if all you need is regex matching) Also there’s OgreKit

Does the search string \bhi\b not work - is \b ommitted from the implementation? If so, are there any other ways to achieve the same effect?