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


From: Ed Morton
Subject: Re: Quickie - Regexp for a string not at the beginning of the line
Date: Fri, 26 Oct 2012 07:32:10 -0500
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20121010 Thunderbird/16.0.1

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 <address@hidden> wrote:
Rivka Miller <address@hidden> writes:
On Oct 25, 2:27 pm, Danny <address@hidden> 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.




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