match index notation of file1 to the index of file2 and pull out matching rows

Question

file1 contains multiple alphabetic sequences:

AETYUIOOILAKSJ
EAYEURIOPOSIDK
RYXURIAJSKDMAO
URITORIEJAHSJD
YWQIAKSJDHFKCM
HAJSUDIDSJSIAJ
AJDHDPFDIXSIBJ
JAQIAUXCNC         


        

Answer 1

awk '(NR==FNR){a[$0]=substr($0,length);next}
     { for(key in a) if (a[key] == substr($0,key+0,1)) { print; break }
     }' file2 file1

Here, the array a[key] is a associative array with the following key-value pairs:

key:   value
3T     T
10K    K
...    ...

When processing file2 with the line: (NR==FNR){a[$0]=substr($0,length);next}: we extract the value beforehand so we don't have to do it later on. The index is easily extracted with a math operation. Eg. "10K"+0=10 in Awk.

Processing file1 is done with the next line. Here we just check if the character matches for any of the entries in the associative array.