Hi Sam,

Perl's regex engine finds the left-most match

I would have phrased it like this: like most engines Perl's looks by default for the longest leftmost match.

% stephan@labaule (/home/stephan) %
% echo "okay stephan do test it!" |                                   
+        
> perl -lne 'm!(steph.?)!; print "seen: [$1]\n"'
seen: [stepha]
[download]

Actually POSIX mandates longest possible for alternations as they all start at the same place. The owl book calls that POSIX NFA.

% stephan@labaule (/home/stephan) %
% echo "okay stephan do test it!" | 
> perl -lne 'm!(steph|steph.?)!; print "seen: [$1]\n"'
seen: [steph]
[download]

so yes, perl's is not POSIX NFA (for various efficiency reasons)

Actually not many engines follow POSIX on this, mostly (ugly -- because too ancient) system libraries (on Un*x), ksh's does too, even the Hackerlab library does (on second thought seems normal as it was supposed to be a drop-in replacement for the C lib on Un*x -- and POSIX). Tcl's is hybrid so I am not sure. And every engine after Perl5 birth has essentially copied Perl's.

regards --stephan

by the way ksh notation is interesting (zsh can masquerade as ksh for this if you don't have a ksh to try)