RegExKitLite Expression Question

Question

I'm having trouble coming up with an RegExKitLite expression that will match. I'm parsing a string and I want it to grab everything till it comes upon the first occurrence of a colon

What would be the expression in RegExKitLite to do that?

Thanks!

Answer 1

This regex will match everything from the start until (but excluding) the first colon:

^[^:]*

To include the first colon is as simple as putting it on the end:

^[^:]*:

So, to use either of those with RegexKitLite, you can do:

NSString * firstItem = [someString stringByMatching:@"^[^:]*" capture:0];

Note how there is no parentheses - since * is greedy you can simply use the negated class and use captured group 0 (i.e. the whole match).

It's worth noting that most languages will include functions that allow you to do this with a regular function, for example ListFirst(MyString,':') or MyString.split(':')[0]

I suspect Objective-C has something similar to this ... yep, see here

NSString *string = @"oop:ack:bork:greeble:ponies";
NSArray *chunks = [string componentsSeparatedByString: @":"];

Answer 2

To do this specifically with RegexKitLite, you'll need to do the following:

Add the RegexKitLite.h/.m files to your project

Import RegexKitLite.h into the file where you need to use regular expressions

Use the following to grab the stuff before the colon:

NSString * everythingBeforeTheColon = [someString stringByMatching:@"([^:]*):" capture:1];

Answer 3

I just updated my SO answer here, so I figured I'd use that to benchmark the standard foundation componentsSeparatedByString: and RegexKitLites componentsSeparatedByRegex:. The line of code inside the for() loop for each was (essentially):

NSString *string = @"oop:ack:bork:greeble:ponies";
for() { NSArray *chunks = [string componentsSeparatedByString: @":"]; }
for() { NSArray *chunks = [string componentsSeparatedByRegex: @":"]; }

Times returned were (time is in microseconds per operation):

componentsSeparatedByString: 3.96810us
componentsSeparatedByRegex:  2.46155us

EDIT:

I thought I'd go one better: How to use RegexKitLite to create a NSArray of NSArrays from a string containing multiple lines of colon separated data (ie, /etc/passwd). Modified from the comma separated value example in the RegexKitLite documentation. When finished, the variable splitLinesArray contains the finished product.

NSString   *theString  = @"a:b:c\n1:2:3\nX:Y:Z\n"; // An example string to work on.
NSArray    *linesArray = [theString componentsSeparatedByRegex:@"(?:\r\n|[\n\v\f\r\\x85\\p{Zl}\\p{Zp}])"];
id          splitLines[[linesArray count]];
NSUInteger  splitLinesIndex = 0UL;

for(NSString *lineString in linesArray) { splitLines[splitLinesIndex++] = [lineString componentsSeparatedByRegex:@":"]; }

NSArray *splitLinesArray = [NSArray arrayWithObjects:splitLines count:splitLinesIndex];