$timestandard =  time() - 604800;  # time() will give us the number of seconds since the epoc
				   # time() less 604800 seconds will give us the number of seconds since the epoc 7 days ago
				   

@data=&magic_fucntion_that_opens_the_file_and_gets_the_data();

foreach $d (@data)
{
	push(@save, $d) if $d>$timestandard;
}

#so now all of the entries that are valid (ie. younger than one week old) are in the array @save
#now we print them to the file

open(SEZME, ">my_data_file.txt");
$,="\n";
print SEZME @save;
close SEZME;
undef($,);

#the rest of the script.............