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Re: How do I do this search and replace? [message #172356 is a reply to message #172354]

Mon, 14 February 2011 10:28

The Natural Philosoph
Messages: 993
Registered: September 2010

Karma:

Senior Member

Erwin Moller wrote:
> On 2/14/2011 10:55 AM, The Natural Philosopher wrote:
>> Erwin Moller wrote:
>>> On 2/12/2011 11:51 PM, BootNic wrote:
>>>> On Sat, 12 Feb 2011 13:15:44 -0800 (PST)
>>>> "laredotornado(at)zipmail(dot)com"<laredotornado(at)zipmail(dot)com> wrote:
>>>>
>>>> > I'm using PHP 5. I want to search for all instances of the "\n"
>>>> > character in my $contents variable and replace it with "\r\n".
>>>> > However, I do not want to replace the "\n" if the character
>>>> > immediately before is already a "\r". How would I construct such
>>>> > a search and replace to do this?
>>>>
>>>> http://www.regular-expressions.info/lookaround.html#lookbehind
>>>>
>>>>
>>>> using negative lookbehind
>>>>
>>>> $contents = preg_replace("/(?<!\r)\n/", "\r\n", $contents);
>>>>
>>>>
>>>
>>> One addition: Using the double replacement strategy as described by
>>> Richard is easier to understand (for non-regexp people), but needs 2
>>> sweeps over the content.
>>>
>>> In case performance matters (more specifically: if the $contents is a
>>> huge string, or/and you have to do this replacement many times
>>> sequentially), if might be better to use the above approach from
>>> BootNic, because I expect it will be much faster.
>>>
>>
>> If performance is an issue, code a one pass loop.
>
> That is exactly what BootNic did.
>
>> Preferably inassembler :-)
>
> Sure. ;-)
>
>>
>> regexp processing is not fast.
>
> Compared to what? Assembly?
>

almost anything.

what you need to understand is that general purpose routines like printf
or a regexp, have to do many many tests IN CASE what gets passed to them
contains one of many possibilities.

They are hugely wasteful compared with a routine dedicated to doing but
one or two things.

> Erwin Moller
>
>>
>>
>>> If performance isn't an issue, pick whatever suits you. :-)
>>>
>>> Regards,
>>> Erwin Moller
>>>
>
>

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[Message index]

		How do I do this search and replace? By: laredotornado@zipmail on Sat, 12 February 2011 21:15
		Re: How do I do this search and replace? By: richard on Sat, 12 February 2011 21:20
		Re: How do I do this search and replace? By: Evan Platt on Sat, 12 February 2011 22:09
		Re: How do I do this search and replace? By: sheldonlg on Sat, 12 February 2011 23:59
		Re: How do I do this search and replace? By: Tim Streater on Sun, 13 February 2011 00:08
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 00:24
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 00:40
		Re: How do I do this search and replace? By: richard on Sun, 13 February 2011 01:03
		Re: How do I do this search and replace? By: richard on Sun, 13 February 2011 00:58
		Re: How do I do this search and replace? By: richard on Sun, 13 February 2011 00:57
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 01:14
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 01:23
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 01:29
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 01:38
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 01:54
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 02:00
		Re: How do I do this search and replace? By: spambait on Sun, 13 February 2011 13:16
		Re: How do I do this search and replace? By: The Natural Philosoph on Sun, 13 February 2011 13:33
		Re: How do I do this search and replace? By: me on Sun, 13 February 2011 13:45
		Re: How do I do this search and replace? By: sheldonlg on Sun, 13 February 2011 13:48
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 13:51
		Re: How do I do this search and replace? By: spambait on Mon, 14 February 2011 01:58
		Re: How do I do this search and replace? By: Denis McMahon on Mon, 14 February 2011 02:25
		Re: How do I do this search and replace? By: The Natural Philosoph on Mon, 14 February 2011 09:51
		Re: How do I do this search and replace? By: sheldonlg on Mon, 14 February 2011 12:50
		Re: How do I do this search and replace? By: Jerry Stuckle on Mon, 14 February 2011 12:58
		Re: How do I do this search and replace? By: Denis McMahon on Mon, 14 February 2011 15:34
		Re: How do I do this search and replace? By: Jerry Stuckle on Mon, 14 February 2011 17:57
		Re: How do I do this search and replace? By: spambait on Sun, 13 February 2011 01:48
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 02:01
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 02:05
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 02:13
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 02:33
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 02:44
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 02:49
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 02:53
		Re: How do I do this search and replace? By: me on Sun, 13 February 2011 13:32
		Re: How do I do this search and replace? By: The Natural Philosoph on Sun, 13 February 2011 13:37
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 13:53
		Re: How do I do this search and replace? By: Denis McMahon on Sun, 13 February 2011 04:16
		Re: How do I do this search and replace? By: richard on Sun, 13 February 2011 04:34
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 04:50
		Re: How do I do this search and replace? By: richard on Sun, 13 February 2011 05:35
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 06:11
		Re: How do I do this search and replace? By: sheldonlg on Sun, 13 February 2011 13:19
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 13:56
		Re: How do I do this search and replace? By: Evan Platt on Sun, 13 February 2011 15:09
		Re: How do I do this search and replace? By: Jerry Stuckle on Sun, 13 February 2011 15:19
		Re: How do I do this search and replace? By: Denis McMahon on Sat, 12 February 2011 22:03
		Re: How do I do this search and replace? By: BootNic on Sat, 12 February 2011 22:51
		Re: How do I do this search and replace? By: The Natural Philosoph on Sun, 13 February 2011 00:21
		Re: How do I do this search and replace? By: Curtis Dyer on Mon, 14 February 2011 09:01
		Re: How do I do this search and replace? By: The Natural Philosoph on Mon, 14 February 2011 09:54
		Re: How do I do this search and replace? By: Erwin Moller on Mon, 14 February 2011 09:14
		Re: How do I do this search and replace? By: The Natural Philosoph on Mon, 14 February 2011 09:55
		Re: How do I do this search and replace? By: Erwin Moller on Mon, 14 February 2011 10:04
		Re: How do I do this search and replace? By: The Natural Philosoph on Mon, 14 February 2011 10:28
		Re: How do I do this search and replace? By: Curtis Dyer on Mon, 14 February 2011 10:40

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