String separation in unix shell - bash

Question

STRINGS=str1,str2,str3
I want each string seperated by space as given below:
STRING1=`echo $STRINGS | cut -d',' -f1` ==> gives "str1"
REMAINING_STRING=`echo $STRINGS | cut -d',' -f2- |
sed -e 's/,/ /g'` ==> gives "str2 str3"
But when the string contains only one entry, for e.g STRINGS=str1 , then REMAINING_STRING is also populating with same value as STRING1. I want REMAINING_STRING to be null when the STRINGS contain only one entry.
STRINGS=str1
STRING1=`echo $STRINGS| cut -d',' -f1` ==> gives "str1"
REMAINING_STRING=`echo $STRINGS | cut -d',' -f2- | sed -e 's/,/ /g'`
==> gives "str1", But this should come as null.
How to do this in unix shell?

Answer 1

$ STRINGS=str1
$ echo $STRINGS | cut -d',' -f2- | sed -e 's/,/ /g'
str1
$ echo $STRINGS | cut -s -d',' -f2- | sed -e 's/,/ /g'
$
Explanation of -s from the man page.
-s, --only-delimited
do not print lines not containing delimiters

Answer 2

Use the -a flag of the read command, to split the string into an array. Example:
$ cat script.sh
#!/bin/bash
strings=str1,str2,str3
IFS=, read -ra arr <<< "$strings"
echo "First element: ${arr[0]}"
echo "Second element: ${arr[1]}"
strings=str1
IFS=, read -ra arr <<< "$strings"
echo "First element: ${arr[0]}"
echo "Second element: ${arr[1]}"
$ ./script.sh
First element: str1
Second element: str2
First element: str1
Second element:
The alternative method of splitting the string with
IFS=, arr=($strings)
will also work for most strings, but will fail in there is pathname expansion, E.g. arr=(*) would match all files in the current directory (as konsolebox noted).

Answer 3

Extension of user000001's answer:
$ cat strings.sh
#!/bin/bash
function splitstr {
local a
set -f
IFS=, a=($1); str_first=$a; unset a[0]; str_rest="${a[#]}"
set +f
}
splitstr 'one,*,three,four'; echo -e "<$str_first>\t<$str_rest>"
splitstr 'one'; echo -e "<$str_first>\t<$str_rest>"
splitstr ''; echo -e "<$str_first>\t<$str_rest>"
$ ./strings.sh
<one> <* three four>
<one> <>
<> <>