Quickie - Regexp for a string not at the beginning of the line

[Joel Goldstick]

On Fri, Oct 26, 2012 at 8:32 AM, Ed Morton <mortonspam at gmail.com> wrote:
> On 10/25/2012 11:45 PM, Rivka Miller wrote:
>>
>> Thanks everyone, esp this gentleman.
>>
>> The solution that worked best for me is just to use a DOT before the
>> string as the one at the beginning of the line did not have any char
>> before it.
>
>
> That's fine but do you understand that that is not an RE that matches on
> "$hello$ not at the start of a line", it's an RE that matches on "<any
> char>$hello$ anywhere in the line"? There's a difference - if you use a tool
> that prints the text that matches an RE then the output if the first RE
> existed would be "$hello$" while the output for the second RE would be
> "X$hello$" or "Y$hello$" or....
>
> In some tools you can use /(.)$hello$/ or similar to ignore the first part
> of the RE "(.)" and just print the second "$hello", but that ability and
> it's syntax is tool-specific, you still can't say "here's an RE that does
> this", you've got to say "here's how to find this text using tool
> <whatever>".
>
>    Ed.
>
>
>> I guess, this requires the ability to ignore the CARAT as the beginning of
>> the line.
>>
>> I am a satisfied custormer. No need for returns. :)
>>
>> On Oct 25, 7:11 pm, Ben Bacarisse <ben.use... at bsb.me.uk> wrote:
>>>
>>> Rivka Miller <rivkaumil... at gmail.com> writes:
>>>>
>>>> On Oct 25, 2:27 pm, Danny <dann90... at gmail.com> wrote:
>>>>>
>>>>> Why you just don't give us the string/input, say a line or two, and
>>>>> what you want off of it, so we can tell better what to suggest
>>>
>>>
>>>> no one has really helped yet.
>>>
>>>
>>> Really?  I was going to reply but then I saw Janis had given you the
>>> answer.  If it's not the answer, you should just reply saying what it is
>>> that's wrong with it.
>>>
>>>> I want to search and modify.
>>>
>>>
>>> Ah.  That was missing from the original post.  You can't expect people
>>> to help with questions that weren't asked!  To replace you will usually
>>> have to capture the single preceding character.  E.g. in sed:
>>>
>>>    sed -e 's/\(.\)$hello\$/\1XXX/'
>>>
>>> but some RE engines (Perl's, for example) allow you specify zero-width
>>> assertions.  You could, in Perl, write
>>>
>>>    s/(?<=.)\$hello\$/XXX/
>>>
>>> without having to capture whatever preceded the target string.  But
>>> since Perl also has negative zero-width look-behind you can code your
>>> request even more directly:
>>>
>>>    s/(?<!^)\$hello\$/XXX/
>>>
>>>> I dont wanna be tied to a specific language etc so I just want a
>>>> regexp and as many versions as possible. Maybe I should try in emacs
>>>> and so I am now posting to emacs groups also, although javascript has
>>>> rich set of regexp facilities.
>>>
>>>
>>> You can't always have a universal solution because different PE
>>> implementations have different syntax and semantics, but you should be
>>> able to translate Janis's solution of matching *something* before your
>>> target into every RE implementation around.
>>>
>>>> examples
>>>
>>>
>>>> $hello$ should not be selected but
>>>> not hello but all of the $hello$ and $hello$ ... $hello$ each one
>>>> selected
>>>
>>>
>>> I have taken your $s to be literal.  That's not 100 obvious since $ is a
>>> common (universal?) RE meta-character.
>>>
>>> <snip>
>>> --
>>> Ben.
>>
>>
>
> --
> http://mail.python.org/mailman/listinfo/python-list

I would use str.find('your string')

It returns -1 if not found, and the index if it finds it.

why use regex for this?

-- 
Joel Goldstick