my ( $yr, $mo, $dy ) = (localtime)[5,4,3];
my $outfile = sprintf( "%04d%02d%02d.txt",$yr+1900,$mo+1,$dy );

# (I tend to format date-as-filename so that it will be
# easy to sort file names chronologically:  YYYYMMDD)
# you can add hours and minutes, if you like -- check
# `perldoc -f localtime`...