PHP Regex: Select all except last occurrence

Question

I'm trying to replace all \n's sans that final one with \n\t in order to nicely indent for a recursive function.

This
that
then
thar
these
them

should become:

This
    that
    then
    thar
    these
them

This is what I have: preg_replace('/\n(.+?)\n/','\n\t$1\n',$var);

It currently spits this out:

This
    that
then
thar
these
them

Quick Overview:

Need to indent every line less the first and last line using regex, how can I accomplish this?

It's not possible that that code produces that output.... [and it doesn't](http://codepad.org/f9SiMGm4). — Lightness Races in Orbit, Oct 10 '11 at 21:32
@Korvin: What? That's the OP's example. Of course it fails, or else he would not be here. I'm merely demonstrating that it fails in a different way to what the OP claimed. — Lightness Races in Orbit, Oct 10 '11 at 21:37
@Korvin: I just noticed that _you're_ the OP, so it's _your_ example. Bizarre. — Lightness Races in Orbit, Oct 10 '11 at 21:40

score 3 · Answer 1 · answered Oct 10 '11 at 21:33

3

You can use a lookahead:

$var = preg_replace('/\n(?=.*?\n)/', "\n\t", $var);

See it working here: ideone

answered Oct 10 '11 at 21:33

Mark Byers

811,555
193
1,581
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score 2 · Accepted Answer · answered Oct 10 '11 at 21:35

After fixing a quotes issue, your output is actually like this:

This
    that
then
    thar
these
them

Use a positive lookahead to stop that trailing \n from getting eaten by the search regex. Your "cursor" was already set beyond it so only every other line was being rewritten; your match "zones" overlapped.

echo preg_replace('/\n(.+?)(?=\n)/', "\n\t$1", $input);
//          newline-^  ^-text ^-lookahead ^- replacement

Live demo.

score 1 · Answer 3 · answered Oct 10 '11 at 21:31

1

preg_replace('/\n(.+?)(?=\n)/',"\n\t$1",$var);

Modified the second \n to be the lookahead (?=\n), otherwise you'd run into issues with regex not recognizing overlapping matches.

http://ideone.com/1JHGY

answered Oct 10 '11 at 21:31

Amber

507,862
82
626
550

score -1 · Answer 4 · answered Oct 10 '11 at 22:07

-1

Let the downwoting begin, but why use regex for this?

<?php
$e = explode("\n",$oldstr);
$str = $e[count($e) - 1]; 
unset($e[count($e) - 1]);
$str = implode("\n\t",$e)."\n".$str;
echo $str;
?>

Actually, str_replace has a "count" parameter, but I just can't seem to get it to work with php 5.3.0 (found a bug report). This should work:

<?php
$count = substr_count($oldstr,"\n") - 1;
$newstr = str_replace("\n","\n\t",$oldstr,&$count);
?>

answered Oct 10 '11 at 22:07

Marius Solbakken Mellum

636
5
10

1

Why go through all that when a regex will let you do it in one line of code? – Alan Moore Oct 11 '11 at 08:43
1

@AlanMoore Not to mention the regex can easily be applied to another language. – user137369 Jul 03 '15 at 17:40

PHP Regex: Select all except last occurrence

Quick Overview:

4 Answers4

Live demo.

Linked