[28595] trunk/dports/math/bc/Portfile

[Ryan Schmidt]

On Sep 5, 2007, at 06:33, Weissmann Markus wrote:

> On 05.09.2007, at 11:58, Ryan Schmidt wrote:
>
>> On Sep 4, 2007, at 03:34, source_changes at macosforge.org wrote:
>>
>>> Revision: 28595
>>>           http://trac.macosforge.org/projects/macports/changeset/ 
>>> 28595
>>> Author:   mww at macports.org
>>> Date:     2007-09-04 01:34:17 -0700 (Tue, 04 Sep 2007)
>>>
>>> Log Message:
>>> -----------
>>> take maintainership, add sha1 checksum & livecheck
>>
>> [snip]
>>
>>> +
>>> +livecheck.check  regex
>>> +livecheck.url    http://ftp.gnu.org/gnu/bc/?C=M&O=D
>>> +livecheck.regex  bc-(\[0-9\.\]+\[0-9\])\\.
>>> +
>>
>> You don't need a backslash before a period in a character class. So
>>
>> 	livecheck.regex  bc-(\[0-9.\]+\[0-9\])\\.
>>
>> would be better.
>
> O.k., but what does the backslash do then before a period? Nothing?

The string you write in your portfile is:

	bc-(\[0-9.\]+\[0-9\])\\.

so that the string Tcl hands to the regex interpreter is:

	bc-([0-9.]+[0-9])\.

In a regex in the portfile, one backslash escapes the next character  
from the Tcl interpreter. A period has no special meaning in Tcl, so  
"\." is the same as ".".

At the end of your regex, you have "\\.". The first backslash removes  
the special meaning of the second backslash so that the regex engine  
sees "\." which in turn tells the regex engine to remove the special  
meaning of the period, so that instead of matching any character, it  
matches a literal period only.

Within a regular expression, a period only has the special meaning of  
matching any character when the period occurs outside of a character  
class. Inside a character class, a period means a literal period. So  
the regex character class "[0-9.]" does not mean "match the  
characters zero thru nine and any character"; rather, it means "match  
the characters zero thru nine and the period".