Iterate over an array using POSIX Shell

iterate_shell_array.sh

#!/bin/sh
# Iterate over an array using POSIX Shell

# Initial data
ARR="a:b:c:d"

# Iteration. Do whatever is needed instead of 'echo "$VAL"'.
CDR="${ARR}:"; while [ -n "$CDR" ]; do CAR=${CDR%%:*}; echo "$CAR"; CDR=${CDR#*:}; done; unset CAR CDR

# IMPORTANT!!! Add semicolon to the end of an array (IT="${ARR}:") to make stop condition working.
#              Otherwise you will get infinite loop.

Nice work! I always tough that prefix/suffix removing in variables is Bash-ism. I would never think of this solution. Again, nice work..
I have took your code and move it into function, here is preview (It's just an idea, still not finished)...
Usage: for_each $ARR do echo for print every element
Code:

for_each () {
   test "$2" == "do" \
     || return 1
   ARR="$1:"
   while test -n "$ARR" ; do
     CAR=${ARR%%:*}
     eval $3 "$CAR"
     ARR=${ARR#*:}
   done
   unset CAR ARR
}

Yes, nice work!

Forked and revised: you forgot to change $VAL to $CAR in the comment of line 7, at revision 5.