There is another solution :
just run the program map with parameter -open=n
It will translate only open reading frames of at least n amino acids
wide. Finding the start codons is then easy.
If you want to find also the GUG start codons, "fetch" the file
enzyme.dat and put the valine codon GTG in lowercase (gtg). Idem
for UUG. Note that map will write V in the translation, since
the program does not "know" it should be methionine or