The above didn't work for me. $\ is undefined by default so the newline doesn't print and $= is 60 by default so the tests fail. This is the best fix I could come up with, unfortunately with one extra character:

@ARGV='ctriangle.txt';sub n{print
" "x(40-$r/2)."$x\n"};$/=$w;$_=<>;
($r=length($x.=" $_"))>$/and
$/=$r,n,$x=''for split;n;
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