Add a string at the end of a string for a particular string inside a String

Question

I have a big string that contains several strings like the following:

http://website.com/image.jpg and I want to add ?w=100 to each of them.

So far I thought about creating a regular expression where every time I would encounter that string, it would replace it by the same string with the ?w=100 added to it.

Here is an extension of String to replace the string:

public func stringByReplacingMatches(matchRegEx: String, withMatch: String) -> String {
    do {
        let regEx = try NSRegularExpression(pattern: matchRegEx, options: NSRegularExpressionOptions())
        return regEx.stringByReplacingMatchesInString(self, options: NSMatchingOptions(), range: NSMakeRange(0, self.characters.count), withTemplate: withMatch)
    } catch {
        fatalError("Error in the regular expression: \"\(matchRegEx)\"")
    }
}

And this is how I use it:

myString.stringByReplacingMatches("https:\\/\\/website\\.com\\/[\\w\\D]*.jpg", withMatch: "https:\\/\\/website\\.com\\/[\\w\\D]*.jpg?w=100"))

Problem, this is what I get after replacing the string:

https://website.com/[wD]*.jpg?w=100

How can I solve my problem?

Jeffery Thomas · Accepted Answer · 2016-03-04 10:58:42Z

1

You need to learn about capture groups:

myString.stringByReplacingMatches("(https:\\/\\/website\\.com\\/[\\w\\D]*.jpg)", withMatch: "$1?w=100")

Oh and don't forget to save the return value

let fixedString = myString.stringByReplacingMatches("(https:\\/\\/website\\.com\\/[\\w\\D]*.jpg)", withMatch: "$1?w=100")

myString will not change, but fixedString will have all the updates.

UPDATE

[\\w\\D]* matches any character. You need to craft a more specific regular expression.

For the input "https://website.com/x.jpg" "https://website.com/x.jpg", the regex \w works.

var myString = "\"https://website.com/x.jpg\" \"https://website.com/x.jpg\""
myString = myString.stringByReplacingMatches("(https:\\/\\/website\\.com\\/\\w*.jpg)", withMatch: "$1?w=100")

But this will not work for every possible URL.

edited Mar 4, 2016 at 10:58

answered Mar 4, 2016 at 3:16

Jeffery Thomas

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5 Comments

paulvs Over a year ago

Why do you need a capture group if you can use $0 to insert the matched string?

Jeffery Thomas Over a year ago

@paulvs I prefer to be explicit. $0 works, but is less flexible.

Nico Over a year ago

It works thanks but only for the last occurrence. How can I make it work for all the occurrences in my big string? I guess the regex is fine, it's probably the function.

Jeffery Thomas Over a year ago

@Nico \w matches any word, \D matches any non-digit. Between the two, it matches every character. You need a better regular expression.

Nico Over a year ago

Yes I realised it afterwards... I ended up using this regex: [\\w-$+()*!']*. Might need to get a better one though. Thanks

wottle · Accepted Answer · 2016-03-04 03:28:41Z

1

You should call it as

myString.stringByReplacingMatches("https:\\/\\/website\\.com\\/[\\w\\D]*.jpg", withMatch: "$0?w=100"))

The template can use $0 to show the matching string. You should not repeat the matching regular expression there.

answered Mar 4, 2016 at 3:28

wottle

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3 Comments

Nico Over a year ago

It works thanks but only for the last occurrence. How can I make it work for all the occurrences in my big string? I guess the regex is fine, it's probably the function.

wottle Over a year ago

Your matchign expression is too broad. Try

myString.stringByReplacingMatches("http:\\/\\/[a-zA-Z0-9]*.[a-zA-Z0-9]*\\/[a-zA-Z0-9]*.[a-zA-Z0-9]*", withMatch: "$0?w=100"))

That may work from some URLs, but I would look for a better regular expression to detect all different types of URLs. For your original question, the template change is the correct solution. The correct matching of URLs in a larger string is a different question altogether.

Nico Over a year ago

Yes I realised it afterwards... I ended up using this regex: [\\w-$+()*!']*. Might need to get a better one though. Thanks

paulvs · Accepted Answer · 2016-03-04 03:15:37Z

0

do {
    let regex = try NSRegularExpression(pattern: "http:\\/\\/[a-z]*.[a-z]*\\/[a-z]*.[a-z]*", options: .CaseInsensitive)
    var newString = regex.stringByReplacingMatchesInString(a, options: NSMatchingOptions(rawValue: 0), range: NSMakeRange(0, a.characters.count), withTemplate: "$0?w=100")
    print(newString)
}

answered Mar 4, 2016 at 3:15

paulvs

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