I’ve shown previously how to rename many files on the command line. That solution required a 2nd textfile in the format oldname<space>newname<return>.
Sometimes it is easier if there is no external file and we simply want to iterate over a list that is part of the script. The command to use in this case is called set, which will split on the character in the variable IFS (=internal field separator?).
for i in a,b c,d ; do IFS=","; set $i; echo $1 $2; done
a b c d