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Re: How do I do this search and replace? [message #172359 is a reply to message #172347]

Mon, 14 February 2011 10:40

Curtis Dyer
Messages: 34
Registered: January 2011

Karma:

Member

Erwin Moller
<Since_humans_read_this_I_am_spammed_too_much(at)spamyourself(dot)com>
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?
>>
>> [url][/color]
[color=teal]>> http://www.regular-expressions.info/lookaround.html#lookbehind[/color]
[color=teal]>> [/url] [/color]
>>
>> 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.

That was my hypothesis as well. I did some rudimentary
benchmarking and found that using the two-pass approach was
actually consistently faster (even when I altered both versions to
account for single CRs):

/* based on richard's proposed solution */
function twopass($str)
{
$str = str_replace("\r\n", "\n", $str);
return str_replace("\n", "\r\n", $str);
}

The data:

$data = "Foo bar baz,\n"
. "Quux baz bar foo!\r\n"
. "Line ending with a carriage return.\r"
. "Foo bar baz.\n";
$data = str_repeat($data . str_repeat("\n", 500), 10000);

Of course, YMMV. I didn't bother to do very thorough testing.

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

Exactly.

--
Curtis Dyer
<?$x='<?$x=%c%s%c;printf($x,39,$x,39);?>';printf($x,39,$x,39);?>

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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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