How to split a single line of fields delimited by commas into multiple lines with a specific number of fields in each line?

Another approach with tr and paste:

For n=2,

$ <input tr ',' '\n' | paste -d ',' - - Hello,Hi Hullo,Hammers Based,Random 

For n=3,

$ <input tr ',' '\n' | paste -d ',' - - - Hello,Hi,Hullo Hammers,Based,Random 

Using perl:

$ echo 'Hello,Hi,Hullo,Hammers,Based,Random' | perl -F, -le ' BEGIN { $n = shift }; for ($i=0; $i < @F; $i += $n) { print join(",", @F[$i .. ($i + $n - 1)]); }' 2 Hello,Hi Hullo,Hammers Based,Random 

This uses the first argument as the number of entries printed per output line (using variable $n). STDIN and any filename arguments are used as the input.

Due to the -F, option (which implicitly enables the -a and -n options), it automatically reads each input line and splits it on commas into array @F, then iterates over the indices of the array, $n items at a time. $n elements are printed on each output line.

NOTE: use the Text::CSV module if you need to parse actual CSV with quoted fields and commas embedded in quotes rather than simple comma-delimited input.

Output with an argument of 3 instead of 2:

$ echo 'Hello,Hi,Hullo,Hammers,Based,Random' | perl -F, -le 'BEGIN{$n = shift};for($i=0;$i<@F;$i+=$n){print join(",",@F[$i..($i+$n-1)])}' 3 Hello,Hi,Hullo Hammers,Based,Random 

And again with 4:

$ echo 'Hello,Hi,Hullo,Hammers,Based,Random' | perl -F, -le 'BEGIN{$n = shift};for($i=0;$i<@F;$i+=$n){print join(",",@F[$i..($i+$n-1)])}' 4 Hello,Hi,Hullo,Hammers Based,Random,, 

sed 's/,/\n/2;P;D' 

m=3 sed "s/,/\\n/$m;P;D" 

awk again,
input any suite of values separated by , and newlines,
output a fixed-width csv:

awk '{printf((FNR>1?(FNR-1)%n?",":ORS:"")$0)}END{print ""}' RS='[,\n]' n=4 <<END Hello Hi,Hullo,Hammers,Based Random END Hello,Hi,Hullo,Hammers Based,Random 

With perl :

echo 'Hello,Hi,Hullo,Hammers,Based,Random' | perl -ne ' @L = (/,?([^,]*,[^,]*)/g); $"="\n" ; print "@L" ' 

This question make me think to python zip/iter builtin functions:

python3 -c 'from sys import argv as F; J = "\n".join _, sep, data, sz = F L = [*map(sep.join, zip(*[iter(data.split(sep))]*int(sz)))] print(J(L)) ' , "Hello,Hi,Hullo,Hammers,Based,Random" 2 

Using Raku (formerly known as Perl_6)

~$ raku -ne '.put for .split(",").rotor(3);' file 

Sample Input:

Hello,Hi,Hullo,Hammers,Based,Random 

Sample Output with .rotor(3) (from above):

Hello Hi Hullo Hammers Based Random 

Sample Output changing above to .rotor(2):

Hello Hi Hullo Hammers Based Random 

The code above is a bare-bones implementation in Raku (returning single whitespace between columns). The rotor() call determines the number of columns [ see discussion below regarding the difference between rotor() and batch() ]. Just add a call to .join() if you want to join columns using commas, tabs, pipes, etc.:

~$ raku -ne '.join(",").put for .split(",").rotor(2);' file Hello,Hi Hullo,Hammers Based,Random 

Note, by default rotor() only returns full groups and will drop partial groups at the very end. So perfoming a rotor(4) call on the above six-element sample will result in a single line of output, 4 elements long. To ensure no loss of data, use rotor(4, :partial) or batch(4).

~$ raku -ne '.join(",").put for .split(",").rotor(4);' file Hello,Hi,Hullo,Hammers #COMPARE TO: ~$ raku -ne '.join(",").put for .split(",").batch(4);' file Hello,Hi,Hullo,Hammers Based,Random 

Processing by an authentic CSV-parser (e.g. Raku's Text::CSV module) will validate the resulting CSV file. See the URL below for examples.

https://unix.stackexchange.com/a/701805/227738
https://raku.org

Using sed

$ sed -E 's/([^,]*,[^,]*),/\1\ /g' input_file Hello,Hi Hullo,Hammers Based,Random 

$ sed -E 's/(([^,]*,){2}[^,]*),/\1\ /g' input_file Hello,Hi,Hullo Hammers,Based,Random 

Apart from the obvious awk/Perl/sed approach I can recommend Miller

It can extract and modify Text based data very well and is more intuitive to use that it‘s counterparts.