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macOS NSString Regular Expressions

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

text
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

text
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 it stood on 2021-08-07 after a change by Trev, out of the wiki's dump of 2024-05-26. 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.

Revision 2, last changed by WikiArchive .