The poster above has given you a very good logic flow and design for your program. I'll provide a little more on the functions you might want to use.

open(); 
#look up the proper syntax for using the open function to
#open the file
while(<FILEHANDLE>)
{
    my $line = $_; 
    #I always prefer to copy $_ into an actual named
    #variable. Personal preference. Some other monk please
    #correct me if there is a best practice for this. 
}
[download]

With the variable $line, you will want to look at the split() function. This will help you separate out the columns in each line. Also take a look at chomp if one of the columns is at the end of the line. Once you have the columns, abs will help with retrieving the absolute values. Finally, if the column matches your criteria, just print the variable $line. Afterwards, just run your program and redirect to the textfile of your choice.

Happy coding!


N.B. the code I posted has not been tested and thus prone to typos.