No loop but 2 regexps: 

$_="x" x 30;
s:xx:(" " x (length($')/2))."$`$&\n":ge;
s:(?<=\n).*:$&$`$`:s;
print;

[download]
s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

In reply to Re: Resetting pos() within a RegEx? by Skeeve
in thread Resetting pos() within a RegEx? by LanX

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