regex pattern to match string in Objective C

Question

Here is a regex pattern I created in Objective C:

^\n?([#]{1,2}$|[*]{1,2}$|[0-9]{1,3}.$)

I want to match:

starts with \n or empty
ends with # or * or .
if ends with . there will be 1 or 2 or 3 digits in between
If ends with # or *, there could be 1 more # or * in between

The regex I created matches '\n1#' which is not what I want. Can anyone help me correct this? Is this fastest one? The regex will be used frequently, so I want it to be as fast as possible.

UPDATE:

Here's a sample strings for testing:

"\n#", "11*1", "1#", "a1.", "111*", "\n1#", "\n11.", "a11.", "1. ", "*1."

The 1# and 111* were matched. Not sure what went wrong.

Isn't item #1, "Starts with \n or empty" useless? A string that starts with \n is nothing more than an empty line. Instead just search for the string you are looking for with an explicit '^' at the start of your regex. it will simplify the regex just a little bit. — Anil
– Anil, Commented Jan 27, 2013 at 21:50
@SlyRaskal Makes Sense, thanks. Do you know what's the problem with the rest? — Jensen
– Jensen, Commented Jan 27, 2013 at 21:52
Studying it now, don't know if what I'm coming up with will work though. — Anil
– Anil, Commented Jan 27, 2013 at 21:53
I think you need to be more specific on what type of characters should be present when a # or * is at the end. I think that's the problem. Is it that there shouldn't be any numbers but it can be any other character if it ends with # or *? — Anil
– Anil, Commented Jan 27, 2013 at 22:05

Jilouc · Accepted Answer · 2013-01-27 22:12:04Z

1

You're matching #1 and 111# because of [0-9]{1,3}.. You haven't escaped the . and this group basically matches any sequence of 1 to 3 digits followed by any character.

What you're looking for is

^\n?(#{1,2}|\*{1,2}|[0-9]{1,3}\.)$

Properly escaped in ObjC, it would be

@"^\n?(#{1,2}|\\*{1,2}|[0-9]{1,3}\\.)$"

If this regex is used quite a lot, you might want to cache the NSRegularExpression object to avoid compiling it everytime.

Regexpal is very useful to test regular expressions.

answered Jan 27, 2013 at 22:12

Jilouc

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1 Comment

Jensen Over a year ago

I was just about to answer the question myself. I got warning when I added one \. Objective-C requires you to add two \. Thanks.

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