perl -lnE "BEGIN{$aoa[0]=[@ARGV]}$aoa[$.][$x]=$_; if(eof){close ARGV;$x++}END{map{say join ',',@$_}@aoa}" file1.txt file2.txt file3.txt

file1.txt,file2.txt,file3.txt
13,22,38
14,25,30
12,27,32
10,23,35
13,28,34
,25,32
,24,32
,,36