[CMake] How to assign data from subexpressions of regular expressions to CMake variables?

[Michael Wild]

On 01/20/2011 02:14 PM, David Cole wrote:
> On Thu, Jan 20, 2011 at 8:06 AM, Michael Wild <themiwi at gmail.com> wrote:
> 
>> On 01/20/2011 02:01 PM, David Cole wrote:
>>> On Thu, Jan 20, 2011 at 7:39 AM, Michael Wild <themiwi at gmail.com> wrote:
>>>
>>>> On 01/20/2011 12:10 PM, SF Markus Elfring wrote:
>>>>>> Thanks for your help to make CMake better,
>>>>>
>>>>> Is the command variant "string(REGEX REPLACE ...)" completely
>> documented?
>>>>>
>>>>> Can multiple variables be specified that will receive the data from the
>>>>> evaluation of subexpressions in the passed regular expression?
>>>>>
>>>>> Regards,
>>>>> Markus
>>>>
>>>> AFAIK no, but you can "misuse" if(<string|varname> MATCHES <pattern>)
>>>> for this. It stores the groups in CMAKE_MATCH_<n> where <n> is {0..9}.
>>>> Match 0 is always the whole match of <pattern> and match 1 is the
>>>> contains the first group.
>>>>
>>>> Michael
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>>>
>>>
>>> I think it's the case that the CMAKE_MATCH_* variables are set after
>> *any*
>>> regex matching operation, be it from an "if(... MATCHES ...)" or a
>>> "string(REGEX" or "string(MATCH" command. Let us know if you find that
>> not
>>> to be true.
>>>
>>> From the bottom of (
>>> http://cmake.org/cmake/help/cmake-2-8-docs.html#command:string ) :
>>>
>>>   () Saves a matched subexpression, which can be referenced
>>>      in the REGEX REPLACE operation. Additionally it is saved
>>>      by all regular expression-related commands, including
>>>      e.g. if( MATCHES ), in the variables CMAKE_MATCH_(0..9).
>>>
>>>
>>> HTH,
>>> David
>>>
>>
>> Ah, yes. I keep forgetting. Might I propose that the documentation about
>> regular expressions be extracted into its own section and then be
>> referenced from all commands that have a REGEX mode? Because,
>> confusingly, the only documentation about regular expression is at the
>> end of the string(REGEX REPLACE) command, but then uses if(... MATCHES
>> ...) as an example. For the reader of the if( MATCHES ) documentation,
>> this isn't very discoverable, it doesn't even refer him to the
>> string(REGEX REPLACE) command.
>>
>>
>> Michael
>>
> 
> 
> Me too. I had to go searching for "CMAKE_MATCH_" because I knew it was
> stated somewhere. Much to my surprise, there was only a single "CMAKE_MATCH"
> on our whole documentation page. It would make sense to document the
> variables CMAKE_MATCH_0 and friends explicitly. And cross-referencing left,
> right, north and south would also be good.
> 
> You can propose all you want. I keep getting distracted by the "real bugs"
> on my plate...
> 
> :-)
> 

;-) Right. Anyways, some newbie doing serious RTFM as he should will
stumble across the string(REGEX REPLACE) documentation any ways and
connect the dots :-P