#23456789_123456789_123456789_123456789_1234567 (47)
    perl -e'split$,,GATC;print@_[rand 4]for+1..pop' 1000

    #23456789_123456789_123456789_123456789_12345   (45)
    perl -e'print+substr+GATC,4*rand,1for+1..pop'   1000

    #23456789_123456789_123456789_123456789_12      (42)
    perl -e'print+(G,T,A,C)[rand 4]for+1..pop'      1000