Player(Squre) move along fixed line (which can be straight , incline, circuler etc) with inputs of joystick !

hello, I am trying to make game in which`there is line created by me before the start of game(not like in running game) and player(Squre) only can move along that line by joystick like if I go forward in joystick it go forward in line , if I go backward it goes backward in line , if I go up or down it turn in the line( if there is any turn). That means that forward, backward, up,down is globally and also if my line is in horizontal direction and i pull joystick up then it will not move from the line in vertical direction of line path. so, it is like line following (with input ). so, what kind of code it has to take.. I don't know whether I use boxcolider on adjacent to line or anything else after using box collider it does not look good so what should I use for this type of problem? Thank you for Advance!