Pattern Recognition in comparison

Pattern Recognition in comparison

I am totally new to pattern matching or recognition. My question is that,
if I have a series of strings, say, str1: ABCAAAAAAAEFG, str2:
ABCBBBBBBBBCC, str3: SSSCCCCCCCCEFG, etc. I want to compare the strings
and find out the shared patters in same positions.
For example, I want to compare str1 with str2, the result of the matching
is that there is shared pattern: ABC from the beginning. The second step
is to compare str1 with str3, the result is that there is a shred pattern:
EFG from the end. I want to make this comparison for every two pairs in my
set: (str1,str2), (str1,str3), (str2, str3). etc.
How can I do this programmatically. My question may be too general, but I
am totally new to this area and I need to know some tools or functions if
possible that can help me to do this efficiently.