Clear all not working and blank plot found?

%% I am trying to run this type program

clc

clear all

close all

syms x output

x=linspace(1,2,3)

output=sin(pi*x./4)

plot(x,output)

%% but i found blank plot and this type of error

Error using clear

CLEAR can only clear the import list in the base workspace

Error in test (line 3)

clear all