awk Compare 2 files, print match and difference

Question

I need to comapre two files f1.txt and f2.txt and obtain matches, and non-matches, for this case I am looking to match first field on both files. And print first the second field of f2.txt, then print the entire line of f1.txt. And for no match found on f2.txt to state "Not Found" and then print f1.txt entire line.

F1.txt

1;2;3;4;5;6;7;8
1a;2;3;4;5;6;7;8
1b;2;3;4;5;6;7;8
2b;2;3;4;5;6;7;8

F2.txt

1;First
1a;Firsta
1b;Firstb

Desired output:

First;1;1;2;3;4;5;6;7;8
Firsta;1a;1a;2;3;4;5;6;7;8
Firstb;1b;1b;2;3;4;5;6;7;8
Not Found;2b;2;3;4;5;6;7;8

I am able to obtain the matches but not the non match

awk -F ";" -v OFS="";"" "NR==FNR{a[$1]=$2;next}a[$1]{print a[$1],$0}" f2.txt f1.txt

Thanks

Answer 1

This should do:

awk -F";" 'NR==FNR{a[$1]=$2;next}{if (a[$1])print a[$1],$0;else print "Not Found", $0;}' OFS=";" f2.txt f1.txt

Answer 2

This was very useful . I have changed a bit to get data between 2 files and only have 1 column in each file .

awk 'BEGIN { OFS=FS=";" } FNR==NR { array[$1]=$1; next } { print ($1 in array ? array[$1] : "Not Found"), $0 }' file1 file2