[Newbies] Re: Lookaround Regex to manipulate Strings

[Andreas Raab]

Hans Gruber wrote:
> Hi Guys!
> 
> Thank you so much, this worked fine!

You're welcome. Do yourself a favor and browse around a little in the 
various String protocols. There's a *ton* of useful stuff like 
allButFirst:, allButLast:, copyUpTo:, copyUpToLast:, copyAfter:, 
copyAfterLast: etc. So for example:

   baseName := fileName allButLast: 4. "strips off .foo if you know it's 
3 chars but copyUpToLast: is safer here"
   extension := fileName copyAfterLast: $. "gets the .extension"

etc.

Cheers,
   - Andreas


> Regards,
> Hans
> 
>> Hans Gruber wrote:
>>> Hi Squeak Fans!
>>>
>>> I have a short question regarding regular expressions in Squeak.
>>>
>>> I have the following problem:
>>>
>>> I have a fileName and I want to cut off its file extension (.jpg, .png etc.). To do this efficiently I wanted to use regular expressions with lookaround.
>> Using regular expressions may be convenient, it sure as hell isn't 
>> efficient. Much easier to use, e.g.,
>>
>>    fileName copyUpToLast: $.
>>
>> As for efficiency:
>>
>> [1 to: 10000 do:[:i|
>> 	'filename.jpg' matchesRegex: '.+(=?.(jpg|jpeg|png))'
>> ]] timeToRun.
>> => 2222 msecs
>>
>> [1 to: 10000 do:[:i|
>> 	'filename.jpg' copyUpToLast: $.
>> ]] timeToRun.
>> => 30 msecs
>>
>> So using regexp's is about 80x slower.
>>
>> Cheers,
>>    - Andreas
>>
>>
>>> So let's assume the following:
>>>
>>> | fileName |
>>> fileName := 'test.jpg'.
>>>
>>> fileName matchesRegex: '.+(=?.(jpg|jpeg|png))'
>>>
>>> I thought there is a possibility of returning the string without file extension through lookaround.
>>>
>>> Do you have any hints for me?
>>>
>>> Thanks guys!
>>>
>>> Regards,
>>> Hans
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