my $time_zone_func =
   $file =~ /^London/
      ? \&CORE::gmtime
      : \&CORE::localtime;

strftime($date_format, $time_zone_func->(time))

##</code><code>##

my $time_zone_func =
   $file =~ /^London/
      ? sub { gmtime($_[0]) }
      : sub { localtime($_[0]) };

strftime($date_format, $time_zone_func->(time))

##</code><code>##

my $time_zone_func = sub {
   $file =~ /^London/
      ? gmtime($_[0])
      : localtime($_[0])
};

strftime($date_format, $time_zone_func->(time))