Are you allowed to use a folding cane and unfold it ON SHABBAT, it has a strong rubber string which holds it in plane as a cane?
We are allowed to fold and unfold a cane on shabbos, the same way we are allowed to use a folding chair. It is not considered making a kli because it is meant to be folded and unfolded on a constant basis, therefore it isn’t considered making a kli. Regarding walking outside with it, in a place that doesn’t have an eruv, will depend if the person can’t walk without it, and needs the cane and uses it even to get around the house, then it may be used outside also, however if he doesn’t need it for walking short distances ,such as inside the house, then he may not use it outside without an eruv. (People that need a cane all the time will usually not use a folding one, because there is no need to fold it and put it away!)
O:Ch 315-5, 301-17.