There's no call to join in that call. You have a string constructor and an assignment.

Presuming from the (??{ }), the string will later be interpolated into a regex pattern, at which point a match against that pattern could call join, but it won't be the join you descrived. It will be 

join q{|}, XXX \@{YYY}

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where XXX is the contents of $quotemeta and YYY is contents of $var_name joined by spaces. Double quoted strings (qq{}) interpolate. 

my $quotemeta = 'XXX';
my $var_name = 'YYY';
my $perl5patt = qq{(??{join q{|}, $quotemeta \@{$var_name}})};
print $perl5patt, "\n";

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(??{join q{|}, XXX @{YYY}})

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Since you didn't specify what $quotemeta and $var_name contain, we can't tell if the code executed by the regex engine will match join EXPR, LIST or not.

In reply to Re: what does this code do? by ikegami
in thread what does this code do? by 7stud

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