strftime needs a list of values. You call localtime in scalar context, making it return just a pre-formatted string version of the time. Either use an array to hold the return value

my @systime = localtime( $mtime );
my $str = strftime( "%a %b %e %H:%M:%S %Y", @systime );
[download]

or call localtime when you call strftime

my $str = strftime( "%a %b %e %H:%M:%S %Y", localtime( $mtime ) );
[download]