Do you mean this?
Then...
$1 = some text blablabla THIS
$2 = POSITION
$3 = I
$4 = WANT blablabla blablabla
Though for this exercise it's probably counter-productive. >.>
You probably want $matchtok. If the string with the slash(es) in it contains no spaces you can simply use $matchtok($1-,/,1,32). If it does, you can first return the number of matches with $matchtok($1-,/,0,32) and then return all matches.
$findtok($1-,$matchtok($1-,/,1,32),1,32) would return the position (tokenized by the default space character) of the first match.