Question

I want to insert a comma after the first column and as well as before the last column of all the lines of a file in which each line has a varying number of fields.

E.g. this is file:

test1 test2 test3
test1 test2 test3 test4 test5 test6
test1 test2 test3 test4 
test1 test2 test3 test4 test5

I want to make it look like:

test1, test2, test3
test1, test2 test3 test4 test5, test6
test1, test2 test3, test4 
test1, test2 test3 test4, test5

I ma trying something like following but it is not working (either syntax error OR no expected output):

awk '{NF=NF-1;for (i=NF; i==NF; i--) $i="," print $NF }' my_file1

Answer 1

You don’t need that for-loop. You’re just changing two fields.

I find newlines (and other whitespace) can make awk (and other languages) a whole lot more readable:

% awk '{
    $1 = $1","
    $(NF - 1) = $(NF - 1)","
    print
}
' my_file1
test1, test2, test3
test1, test2 test3 test4 test5, test6
test1, test2 test3, test4
test1, test2 test3 test4, test5