can somebody please explain to me whats the "o" means.

In interpolating patterns, /o will only interpolate once, the first time the regex is evaluated. 

for my $x (qw( foo bar )) {
   /$x/o;
}

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is the same as 
/foo/;
/foo/;

[download]

It's used for optimising, but it's made rather useless by qr//.

In reply to Re: A regular expression (or regex) by ikegami
in thread A regular expression (or regex) by anakin30

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