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Revision 3 of 3, by Trev on 8-7-2021. The page as it is now.

macOS NSString Regular Expressions

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This article applies to macOS only.

See also: Multiplatform Programming Guide

Regular expressions

Regular expressions are patterns used to match specified alpha-numeric character combinations in the string data being searched.

Each character in a regular expression (that is, each character in the string describing its pattern) is either a metacharacter or operator, having a special meaning, or a regular character that has a literal meaning.

Regular expressions can be incredibly complex. Indeed, whole books have been written about them! For a gentle introduction to regular expressions, see this O'Reilly article.

NSString Regular Expression Overview

It is a little known fact that you can use regular expressions to match and replace patterns without having to resort to the more sophisticated, but complicated, NSRegularExpression: NSString has the rangeOfString:options:range: method for matching patterns and the stringByReplacingOccurrencesOfString:withString: method for replacing patterns. These are demonstrated in the examples below.

Metacharacters

For a comprehensive list of characters used that have a special meaning in regular expression patterns, see the ICU listing.

Operators

For a comprehensive list of regular expression operators, see the ICU listing.

Example 1 - match a pattern

Code

pascal
Program regex_ex1;
    
    {$mode objfpc}{$H+}
    {$modeswitch objectivec2}
    
    Uses
      MacOSAll, CocoaAll, SysUtils;
    
    Var
      srchStr : String;
      patnStr : String;
      i: NSRange;
      j: NSRange;
    
    Begin
      srchStr := 'I have 43 bags of 60 marbles.';
      patnStr := '\d+';
    
      // Find first match
      i := NSStr(srchStr).rangeOfString_options_range(NSStr(patnStr), (NSRegularExpressionSearch or NSCaseInsensitiveSearch), NSMakeRange(0, srchStr.Length));
    
      // Find second match
      j := NSStr(srchStr).rangeOfString_options_range(NSStr(patnStr), (NSRegularExpressionSearch or NSCaseInsensitiveSearch), NSMakeRange(i.location + i.length, srchStr.Length - (i.location + i.length)));
    
      // Output
      NSLog(NSStr('Search string: %@'), NSStr(srchStr));
      NSLog(NSStr('Pattern string: %@'), NSStr(patnStr));
    
      NSLog(NSStr('Range 1: %@'), NSStringFromRange(i));
      NSLog(NSStr('Location: %d'), i.location);
      NSLog(NSStr('Length: %d'), i.length);
      NSLog(NSStr('Match: %@'), NSStr(srchStr).substringWithRange(i));
    
      NSLog(NSStr('Range 2: %@'), NSStringFromRange(j));
      NSLog(NSStr('Location: %d'), j.location);
      NSLog(NSStr('Length: %d'), j.length);
      NSLog(NSStr('Match: %@'), NSStr(srchStr).substringWithRange(j));
    End.

Output

pascal
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Search string: I have 43 bags of 60 marbles.
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Pattern string: \d+
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Range 1: {7, 2}
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Location: 7
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Length: 2
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Match: 43
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Range 2: {18, 2}
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Location: 18
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Length: 2
    2021-06-15 21:43:49.049 regex_ex1[23182:177970] Match: 60

Example 2 - replace matched pattern

Code

pascal
Program regex_ex2;
      
    {$mode objfpc}{$H+}
    {$modeswitch objectivec2}
    
    Uses
      MacOSAll, CocoaAll, SysUtils;
    
    Var
      srchStr : NSString;
      patnStr : NSString;
      resStr  : NSString;
      i: NSRange;
      j: NSRange;
    
    Begin
      srchStr := NSStr('I have 43 bags of 60 marbles.');
      patnStr := NSStr('\d+');
    
      // Find first match
      i := srchStr.rangeOfString_options_range(patnStr, NSRegularExpressionSearch, NSMakeRange(0, srchStr.Length));
    
      // Do first replacement
      resStr := srchStr.stringByReplacingOccurrencesOfString_withString(NSStr('43'), NSStr('forty-three'));
    
      // Find second match
      j := srchStr.rangeOfString_options_range(patnStr, NSRegularExpressionSearch, NSMakeRange(i.location + i.length, srchStr.Length - (i.location + i.length)));
    
      // Do second replacement
      resStr := resStr.stringByReplacingOccurrencesOfString_withString(NSStr('60'), NSStr('sixty'));
    
      // Output
      NSLog(NSStr('Search string: %@'), srchStr);
      NSLog(NSStr('Pattern string: %@'), patnStr);
    
      NSLog(NSStr('Range 1: %@'), NSStringFromRange(i));
      NSLog(NSStr('Location: %d'), i.location);
      NSLog(NSStr('Length: %d'), i.length);
      NSLog(NSStr('Match: %@'), srchStr.substringWithRange(i));
    
      NSLog(NSStr('Range 2: %@'), NSStringFromRange(j));
      NSLog(NSStr('Location: %d'), j.location);
      NSLog(NSStr('Length: %d'), j.length);
      NSLog(NSStr('Match: %@'), srchStr.substringWithRange(j));
    
      NSLog(NSStr('Result: %@'), resStr);
    End.

Output

pascal
2021-06-16 11:41:24.025 regex_ex2[5761:21687] Search string: I have 43 bags of 60 marbles.
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Pattern string: \d+
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Range 1: {7, 2}
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Location: 7
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Length: 2
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Match: 43
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Range 2: {18, 2}
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Location: 18
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Length: 2
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Match: 60
    2021-06-16 11:41:24.026 regex_ex2[5761:21687] Result: I have forty-three bags of sixty marbles.

See also

External links

From the Free Pascal wiki, page "macOS NSString Regular Expressions", as the Internet Archive kept it on 2024-10-04, last changed on 2021-08-08. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.