A simple templating category for NSString. I made a couple of small changes to better suit my needs. (check out the diff to see what)

NSString+Templating.h

#import <Foundation/Foundation.h>

@interface NSString (Templating)

+(NSString*)stringWithTemplate:(NSString*)tpl 
                       fromMap:(NSDictionary*)map;

@end

NSString+Templating.m

#import "NSString+Templating.h"

@implementation NSString (Templating)

+(NSString*)stringWithTemplate:(NSString*)tpl 
                       fromMap:(NSDictionary*)map
{
    NSString* retStr = nil;    
    NSMutableString* buffer = [NSMutableString new];    
    NSScanner* scanner = [[NSScanner alloc] initWithString:tpl];

    // Otherwise spaces right after a bracket expression are skipped
    [scanner setCharactersToBeSkipped:nil];
    NSString* tempString = nil;
    
    while([scanner scanUpToString:@"$[" intoString:&tempString])
    {
        NSString* key = nil;
        NSString* value = nil;
        
        [buffer appendString:tempString];
        if([scanner isAtEnd])
        {
            break;
        }
        
        [scanner scanString:@"$[" intoString:nil];
        [scanner scanUpToString:@"]" intoString:&key];
        [scanner scanString:@"]" intoString:nil];
        
        if(key)
        {
            value = [map objectForKey:key];
        }
        
        if(value)
        {
            // just 'value' does not work for NSNumber etc
            [buffer appendString:[value description]];
        }
        else
        {
            [buffer appendFormat:@"$[%@]", key];
        }   
    }
    
    retStr = [NSString stringWithString:buffer];
    [buffer release];
    [scanner release];
    
    return retStr;    
}

@end

Sample.m

- (void)test
{
    NSString* testTemplate = @"Hello $[name], welcome to $[city].";
    
    NSString* testString = [NSString stringWithTemplate:testTemplate fromMap:@{@"name" : @"Popcorny", @"city", @"Taipei"}];
    NSLog(@"%@", testString);    
}