如何为 awk 的 output 添加逗号作为分隔符

Question

How do I add a comma as my delimiter for the output of awk

> cat file.csv
col1,col2,col3,col4
col1,col2,col3
col1,col2
col1
col1,col2,col3,col4,col5

This is my attempt:

> awk -F, 'BEGIN{FS=OFS=","} {print $1 $2}' file.csv
    col1col2
    col1col2
    col1col2
    col1
    col1col2
    >

What I want is this

col1,col2
col1,col2
col1,col2
col1,
col1,col2

Below is just for my ref:

> awk -F, '{print $0}' file.csv
col1,col2,col3,col4
col1,col2,col3
col1,col2
col1
col1,col2,col3,col4,col5

> awk -F, '{print $1}' file.csv
col1
col1
col1
col1
col1

> awk -F, '{print $1 $2}' file.csv
col1col2
col1col2
col1col2
col1
col1col2

Answer 1

The statement print $1 $2 prints one output field, the concatenation of $1 and $2 . Hence there will be no OFS output.

What you're looking for is print $1, $2 which prints two distinct fields, and will therefore have the OFS inserted between them. You can see the difference in the following transcript:

pax@styx:~> echo "1 2" | awk 'BEGIN{OFS="-xyzzy-"}{print $1 $2}'
12
pax@styx:~> echo "1 2" | awk 'BEGIN{OFS="-xyzzy-"}{print $1, $2}'
1-xyzzy-2

Answer 2

if you actually want that trailing "," :

 mawk NF=2 FS=, OFS=,

col1,col2
col1,col2
col1,col2
col1,
col1,col2

...without the trailing "," :

 gawk 'NF < 2 || NF = 2' FS=, OFS=,

col1,col2
col1,col2
col1,col2
col1
col1,col2