Validate a string using regex

Question

I want to validate a string to check if it is alphanumeric and contains "-" and "." with the alphanumeric characters. So I have done something like this to form the regex pattern

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"[a-zA-Z0-9\\.\\-]"
                                   options:NSRegularExpressionCaseInsensitive
                                   error:&error];
NSPredicate *regexTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
BOOL valid = [regexTest evaluateWithObject:URL_Query];

App crashes stating that the regex pattern cannot be formed . Can anyone give me a quickfix to what am i doing wrong? Thanks in advance.

- at the end of the character class does not have to be escaped. The regex is valid. However, I'd use ^[a-zA-Z0-9.-]+\\z for this task. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 18, 2016 at 12:19
In any regex engine I've ever dealt with, the . within a character class does not need to be escaped. The - may, though, since it does have special meaning withing a character class (e.g [A-Z]). — Steven Doggart
– Steven Doggart, Commented Nov 18, 2016 at 12:19

Wiktor Stribiżew · Accepted Answer · 2016-11-18 12:28:18Z

3

You must pass a variable of type NSString to the NSPredicate SELF MATCHES:

NSString * URL_Query = @"PAS.S.1-23-";
NSString * regex = @"[a-zA-Z0-9.-]+";
NSPredicate *regexTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
BOOL valid = [regexTest evaluateWithObject:URL_Query];

See the Objective C demo

Note that you need no anchors with the SELF MATCHES (the regex is anchored by default) and you need to add + to match one or more allows symbols, or * to match 0+ (to also allow an empty string).

You do not need to escape the hyphen at the start/end of the character class, and the dot inside a character class is treated as a literal dot char.

Also, since both the lower- and uppercase ASCII letter ranges are present in the pattern, you need not pass any case insensitive flags to the regex.

answered Nov 18, 2016 at 12:28

Wiktor Stribiżew

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AnxiousMan Over a year ago

Let me try .! give me a second

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