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in reply to Perl Idioms Explained - @ary = $str =~ m/(stuff)/g

$num_matches_stuff = $str =~ m/(stuff)/g;
@all_the_matches   = $str =~ m/(stuff)/g;

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In scalar context we get the count of the matches, in array context we get the matches.
No, the former just is not right. You haven't actually tried it, have you? 
$str = "stuff stuff stuff";
$num_matches_stuff = $str =~ m/(stuff)/g;
print $num_matches_stuff;

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Result: 
1

The /g modifier in scalar context is very special. It is intended to be used in a loop, something like this: 

$str = "stuff stuff stuff";
while($str =~ m/(stuff)/g) {
    print "Got one!\n";
}

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Result: 
Got one!
Got one!
Got one!
So in scalar context, it will match at most once at a time — next time around, it'll continue where it left off last time.

Therefore, the returned valued of //g when used in scalar context is either 0, or 1.

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