I'm trying to replace all 's sans that final one with \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('/ (.+?) /',' \t$1 ',$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?

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

Live demo.

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

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

http://ideone.com/1JHGY

You can use a lookahead:

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

See it working here: ideone

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

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