macOS NSString Regular Expressions
│ English (en) │
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
Program regex_ex1;
{$mode objfpc}{$H+}
{$modeswitch objectivec2}
Uses
MacOSAll, CocoaAll, SysUtils;
Var
srchStr : String;
patnStr : String;
i: NSRange;
j: NSRange;
Begin
srchStr := 'I have 43 bags of 60 marbles.';
patnStr := '\d+';
// Find first match
i := NSStr(srchStr).rangeOfString_options_range(NSStr(patnStr), (NSRegularExpressionSearch or NSCaseInsensitiveSearch), NSMakeRange(0, srchStr.Length));
// Find second match
j := NSStr(srchStr).rangeOfString_options_range(NSStr(patnStr), (NSRegularExpressionSearch or NSCaseInsensitiveSearch), NSMakeRange(i.location + i.length, srchStr.Length - (i.location + i.length)));
// Output
NSLog(NSStr('Search string: %@'), NSStr(srchStr));
NSLog(NSStr('Pattern string: %@'), NSStr(patnStr));
NSLog(NSStr('Range 1: %@'), NSStringFromRange(i));
NSLog(NSStr('Location: %d'), i.location);
NSLog(NSStr('Length: %d'), i.length);
NSLog(NSStr('Match: %@'), NSStr(srchStr).substringWithRange(i));
NSLog(NSStr('Range 2: %@'), NSStringFromRange(j));
NSLog(NSStr('Location: %d'), j.location);
NSLog(NSStr('Length: %d'), j.length);
NSLog(NSStr('Match: %@'), NSStr(srchStr).substringWithRange(j));
End.
Output
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Search string: I have 43 bags of 60 marbles.
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Pattern string: \d+
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Range 1: {7, 2}
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Location: 7
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Length: 2
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Match: 43
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Range 2: {18, 2}
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Location: 18
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Length: 2
2021-06-15 21:43:49.049 regex_ex1[23182:177970] Match: 60
Example 2 - replace matched pattern
Code
Program regex_ex2;
{$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
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
- macOS NSRegularExpression.
- RegEx packages - cross platform.
