To avoid the extra variable hanging around, can't you just do:

my $days_re = join('|', @days);
$days_re = qr/$days_re/;
[download]

Of course, I'd like some way to aggregate regular expressions and nicely apply operations like "concatenate" or "alternative" to them without having to drop back into string representations - that is, I'd like to be able to do:

my @days    = qw( Sun Mon Tue Wed Thu Fri Sat ); 
my $days_re = re_alternative(map {qr/\Q$_\E/} @days);
[download]

Right now you have to do this, which is ok I guess, but I wonder if there are efficiency issues with the regular expression constructed this way:

my @days    = qw( Sun Mon Tue Wed Thu Fri Sat );
my $days_re = join("|", map {qr/\Q$_\E/} @days);
   $days_re = qr($days_re);
[download]

--
@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/
map{y/X_/\n /;print}map{pop@$_}@/for@/
[download]