Hi,

Can anyone enlighten me about the usage of the /o option in regular expressions. I have read the documentation (camel book), but this even puzzels me more. f.e. 

my @y=(1..9);
my $x=1;
foreach my $value ( @y ) {
    if ( $value =~ /$x/ ) {
        print "without o\n";
    }
    if ( $value =~ /$x/o ) {
        print "with o\n";
    }
    ++$x;
}

[download]
will print "with o" only once while "without o" 9 times.

So, this means that using /o is the same as fast way precompiling the regex, like you would with qr//?

But what is the difference then?
Perl keeps the pattern compiled in memory as well with a /o as with qr? But with qr, you can access it via a variable, and make it lexical. Is that the only difference?

Is this all correct?


---------------------------
Dr. Mark Ceulemans
Senior Consultant
IT Masters, Belgium

In reply to meaning of /o in regexes by mce

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