Is piping, shifting, or parameter expansion more efficient?

I'm trying to find the most efficient way to iterate through certain values that are a consistent number of values away from each other in a space separated list of words(I don't want to use an array). For example, list="1 ant bat 5 cat dingo 6 emu fish 9 gecko hare 15 i j" So I want to be able to just iterate through list and only access 1,5,6,9 and 15. ***EDIT:*** I should have made it clear that the values I'm trying to get from the list don't have to be different in format from the rest of the list. What makes them special is solely their position in the list(In this case, position 1,4,7...). So the list could be1 2 3 5 9 8 6 90 84 9 3 2 15 75 55 but I'd still want the same numbers. And also, I want to be able to do it assuming I don't know the length of the list. The methods I've thought of so far are: **Method 1** set $list found=false find=9 count=1 while [ $count -lt $# ]; do if [ "${@:count:1}" -eq $find ]; then found=true break fi count=expr $count + 3 done **Method 2** set list found=false find=9 while [ $# ne 0 ]; do if [ $1 -eq $find ]; then found=true break fi shift 3 done **Method 3** I'm pretty sure piping makes this the worst option, but I was trying to find a method that doesn't use set, out of curiosity. found=false find=9 count=1 num=echo $list | cut -d ' ' -f$count while [ -n "$num" ]; do if [ $num -eq $find ]; then found=true break fi count=expr $count + 3 num=echo $list | cut -d ' ' -f$count done ---------- So what would be most efficient, or am I missing a simpler method?