Separate the element after every 2nd ',' and push into next row in bash

Using a Sed loop:

sed -e 's/,/\n/2' -e 'P;D' file

Ex.

$ echo '201012,720,201011,119,201710,16' | sed -e 's/,/\n/2' -e 'P;D'
201012,720
201011,119
201710,16

This replaces the second , with \n, then prints and deletes up the \n, repeatedly until the substitution is no longer successful.

BSD doesn't understand newline as \n in right side of s commands, this is a workaround for ksh,bash,zsh shells:

sed -e :a -e $'s/,/\\\n/2' -e 'P;D' file

Or, a general solution for (old) seds:

sed '
:a
s/,/\
/2
P;D
' file

$ paste -d, - - < <( tr ',' '\n' <file )
201012,720
201011,119
201710,16

or, without the process substitution,

$ tr ',' '\n' <file | paste -d, - -
201012,720
201011,119
201710,16

This replaces all commas in the file with newlines using tr, then uses paste to create two columns separated by a comma from that.

If tr feels a bit too simple, you may replace it with sed 'y/,/\n/', which does the same thing.

I was able to accomplish this with the following awk command:

awk -F, -v OFS=, '{for (i=1;i<=NF;i=i+2) {j=i+1; print $i,$j}}' input

This will loop through each column in the input (incrementing by 2 each iteration) and print that column plus the next adjacent column on a line before moving to the next.

$ cat input
201012,720,201011,119,201710,16
$ awk -F, -v OFS=, '{for (i=1;i<=NF;i=i+2) {j=i+1; print $i,$j}}' input
201012,720
201011,119
201710,16