Question

I have a problem with reading the image path of a string like -> background-image:url(/assets/test.jpg)

I wanna have the string inside of the brackets without the brackets self.

Here is my code used:

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"\\bbackground-image:url\(.*\)\\b" options:NSRegularExpressionCaseInsensitive error:nil];

        thumbnail = [regex stringByReplacingMatchesInString:thumbnail options:0 range:NSMakeRange(0, [thumbnail length]) withTemplate:@"$1"];

what i get is (/assets/test.jpg)

Answer 1

Use the following pattern to get the expeced result:

background-image:url\\((.*)\\)

Applied to your code:

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"background-image:url\\((.*)\\)" options:NSRegularExpressionCaseInsensitive error:nil];

Using this the result will be “/assets/test.jpg”, just as you want it to be.

Your code should have given you a warning about an unknown escape sequence for “\(“. You have to use “\\(” to escape a “(“. Also get rid of “\\b” at the beginning and end of your pattern.

But be aware that this pattern only works when your string only contains “background-image:url(somevaluehere)”

EDIT:

What does \\b mean?

\\b is a word boundary, usually expressed as \b. In an NSString you need to write \\b because you need to escape the \ so it will be treated as real backslash.

Here some information on what word boundaries match:

There are three different positions that qualify as word boundaries:

• Before the first character in the string, if the first character is a
  word character.
• After the last character in the string, if the last character is a word character.
• Between two characters in the string, where one is a word character and the other is not a word character.

Simply put: \b allows you to perform a “whole words only” search using
a regular expression in the form of \bword\b. A “word character” is a
character that can be used to form words. All characters that are not
“word characters” are “non-word characters”.

Taken from http://www.regular-expressions.info/wordboundaries.html

I hope this clarifies this a bit.