Using awk how do I combine data in two files and s

Question

Any ideas how to the following using awk?

Two input files, data.txt and keys.txt:

data.txt contains some data:

A;1
B;2
A;3

keys.txt contains "key;value" pairs ("C" is in this example not part of data.txt, but the awk script should still work):

A;30
B;20
C;10

The output should be as follows:

A;1;30
B;2;20
A;3;30

Hence, each row in data.txt that contains any key from keys.txt should get the corresponding value appended to the row in data.txt.

Answer 1

awk to the rescue!

assumes the second file has unique keys unlike first file (if not you need to specify what happens then)

$ awk 'BEGIN   {FS=OFS=";"} 
       NR==FNR {a[$1]=$2; next} 
       $1 in a {print $0,a[$1]}' file2 file1

A;1;30
B;2;20
A;3;30

ps. note the order of files...

Answer 2

awk solution:

awk -F';' 'NR==FNR{a[$1]=$2; next}{if($1 in a) $0=$0 FS a[$1]; print}' file2 file1

The output:

A1;1;2
A2;2;1
A3;3;0.5
A1;1;2
A2;2;1
A3;3;0.5

---

• NR==FNR - processing the first file i.e. file2

• a[$1]=$2 - accumulating additional values for each key

• if($1 in a) $0=$0 FS a[$1] - appending value if first column matches