"Linux" awk related

Add text content by field

A 3
B 4
C 5
A 8
D 2
C 6

Add the same data as the fields in the above content

awk -F ‘ ‘  ‘{sum[$1]+=$2}END{for(i in sum){print i, sum[i]}}‘  test.txt

Results:

A 11
B 4
C 11
D 2

Stitching two text by field

Text 1:

A 3
B 4
C 5

Text 2:

A high
C Middle
b Low

Stitching two text based on the first field

Results:

A 3 high
B 4 Low
C 5 Middle

Note:
NR: Represents the number of rows that have been read from all files.
FNR: Indicates the number of rows that have been read in the current file.
Give me a chestnut:
There are two files, the first file has 10 lines, the second file has 15 lines. When reading the 5th line of the first file, nr=5,fnr=5. When reading the 8th line of the second file, nr=18,fnr=8.
So NR==FNR means reading the first file.

"Linux" awk related