The program 'pattern' receives as an input parameter from the command line the output of
the 'subseq_fr' program (i.e. a collection of subsequences of equivalent lengths and with
a properly formatted header) and a sequence pattern to match in the begginig of the 
subsequence (i.e. at the 5' end).

The output of this program is given in the standard output, so if you want to use an output 
file you need to redirect the output to a file (in linux you can do this with the '>' symbol).

The output consists of the set of input sequences that match the pattern at their 5' end.

The input header of each sequence is conserved in the output.

This program is open source, and thus every program based on this should be open source as well.