$ cat pm_1205271_bio_fasta_extract_dummy_in.fasta
>1: not wanted - too short
xxxGG
>2: wanted - exact match
xxxxxxxxxxGG
>3: not wanted - not unique
xxxxxxxxxxGGxxxxxxxxxxGG
>4: wanted - unique (but only just)
xxxxxxxxxGGxxxxxxxxxxGG
>5: not wanted - no GG at end
xxxxxxxxxxGGx
>6: not wanted - no match at all
xxxxxxxxxxAA
>7: wanted - match unique
yyyyyyyyyyGGxxxxxxxxxxGG
$ pm_1205271_bio_fasta_extract.pl
$ cat pm_1205271_bio_fasta_extract_dummy_out.fasta
>2: wanted - exact match
xxxxxxxxxxGG
>4: wanted - unique (but only just)
xxxxxxxxxGGxxxxxxxxxxGG
>7: wanted - match unique
yyyyyyyyyyGGxxxxxxxxxxGG