Microsoft Windows [Version 6.1.7600]
C:\Users\x>cd desktop
C:\Users\x\Desktop>try.pl

 Tetra words are:
Use of uninitialized value in addition (+) at C:\Users\x\Desktop\try.pl
 line 8.

 ABCD  ->Starting at pos 1

 BCDE  ->Starting at pos 2

 CDEF  ->Starting at pos 2

 DEFG  ->Starting at pos 2

 EFGH