NSString regular expression find and replace

Question

Building an iOS app that needs to display some HTML string in a UIWebView object. I am trying to search, find for a pattern and replace with the proper link to an image. The image links are original something like [pic:brand:123], where pic is always pic , brand can be any alphanumeric, and the 123 is can also be any non-whitespace alphanumeric.

So far I have tried a few including:

NSString *pattern = @"\\[pic:([^\\s:\\]]+):([^\\]])\\]";

But none has worked for so far.

Here is a sample code:

NSString *str = @"veryLongHTMLSTRING";
NSLog(@"Original test: %@",[str substringToIndex:500]);
NSError *error = nil;
// use regular expression to replace the emoji
NSRegularExpression *regex = [NSRegularExpression
                                  regularExpressionWithPattern:@"\\[pic:([^\\s:\\]]+):([^\\]])\\]"
                                  options:NSRegularExpressionCaseInsensitive error:&error];
if(error != nil){
    NSLog(@"ERror: %@",error);
}else{
    [regex stringByReplacingMatchesInString:str
                                    options:0
                                      range:NSMakeRange(0, [str length])
                               withTemplate:[NSString stringWithFormat:@"/%@/photo/%@.gif",
                                             IMAGE_BASE_URL, @"$1/$2"]];

NSLog(@"Replaced test: %@",[str substringToIndex:500]);

I expect the [pic:brand:123] to be /photo/brand/123.gif. brand is generic here though. It could between anything between numerous options. — shawndreck
– shawndreck, Commented Jan 13, 2013 at 16:19

Martin R · Accepted Answer · 2013-01-13 16:25:35Z

8

I see two errors: There is a + missing in the second capture group of the regex pattern, it should be

NSString *pattern = @"\\[pic:([^\\s:\\]]+):([^\\]]+)\\]";

And stringByReplacingMatchesInString returns a new string, it does not replace the matched string. So you must assign the result to a new string, or use replaceMatchesInString:options:range:withTemplate: with a NSMutableString.

The following modifed code

NSString *pattern = @"\\[pic:([^\\s:\\]]+):([^\\]]+)\\]";
NSString *str = @"bla bla [pic:brand:123] bla bla";
NSLog(@"Original test: %@",str);
NSError *error = nil;
NSRegularExpression *regex = [NSRegularExpression
                              regularExpressionWithPattern:pattern
                              options:NSRegularExpressionCaseInsensitive error:&error];
if(error != nil){
    NSLog(@"ERror: %@",error);
} else{
    NSString *replaced = [regex stringByReplacingMatchesInString:str
                                    options:0
                                      range:NSMakeRange(0, [str length])
                               withTemplate:[NSString stringWithFormat:@"/%@/photo/%@.gif",
                                             @"IMAGE_BASE_URL", @"$1/$2"]];

    NSLog(@"Replaced test: %@",replaced);
}

produces the output

Original test: bla bla [pic:brand:123] bla bla
Replaced test: bla bla /IMAGE_BASE_URL/photo/brand/123.gif bla bla

answered Jan 13, 2013 at 16:25

Martin R

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2 Comments

shawndreck Over a year ago

You are absolutely right, damn I need to stop overworking my eyes! Thanks alot!

user529758 Over a year ago

@shawndreck See my solution as well. :)

user529758 · Accepted Answer · 2013-01-13 16:30:38Z

2

You're misunderstanding how the template should be formed. Also, stringByReplacingMatchesInString doesn't alter the original string. Try this (tested):

NSString *target = @"longHTML [pic:whatever:123] longHTMLcontinues";
NSMutableString *s = [target mutableCopy];

NSError *err = nil;
NSRegularExpression *expr = [NSRegularExpression regularExpressionWithPattern:@"\\[pic\\:([a-zA-Z0-9]*)\\:([a-zA-Z0-9]*)\\]" options:0 error:&err];
if (err) {
    NSLog(@"%@", err);
    exit(-1);
}

[expr replaceMatchesInString:s options:0 range:NSMakeRange(0, s.length) withTemplate:@"/photo/$1/$2.gif"];

answered Jan 13, 2013 at 16:30

user529758

4 Comments

shawndreck Over a year ago

Thanks for heads up. But what I'm confusing with the template? I shouldn't be using [NSString stringWithFormat:....?

user529758 Over a year ago

@shawndreck No. That's unnecessary. The template is a format itself. /photo/$1/$2.gif tells the regex object to substitute the first group in place of $1, etc.

shawndreck Over a year ago

The reason I used stringWithFormat was to be able to include the nsstring constant IMAGE_BASE_URL defined somewhere earlier in my code. I could not simply do /IMAGE_BASE_URL/photo/... because that will only put the literal IMAGE_BASE_URL in my link. Which is definetely not what I am after. But I understand what you have said.

Bruno Bronosky Over a year ago

@shawndreck I see what you are saying about IMAGE_BASE_URL. However, there is no need to substitute in "$1/$2" via string formating. It doesn't change. Take it out of the variable args. Move it to the format string. [NSString stringWithFormat:@"/%@/photo/$1/$2.gif", @"IMAGE_BASE_URL"] Keep It Simple.

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