Engdemo.c not compiling in terminal

Hello,

I am trying to compile the engdemo.c file in terminal but it is not working, and I get this error:

Undefined symbols for architecture x86_64:

"_engClose", referenced from:

_main in engdemo-f79961.o

"_engEvalString", referenced from:

_main in engdemo-f79961.o

"_engGetVariable", referenced from:

_main in engdemo-f79961.o

"_engOpen", referenced from:

_main in engdemo-f79961.o

"_engOutputBuffer", referenced from:

_main in engdemo-f79961.o

"_engPutVariable", referenced from:

_main in engdemo-f79961.o

"_mexPrintf_800", referenced from:

_main in engdemo-f79961.o

"_mxCreateDoubleMatrix_800", referenced from:

_main in engdemo-f79961.o

"_mxDestroyArray_800", referenced from:

_main in engdemo-f79961.o

"_mxGetClassName_800", referenced from:

_main in engdemo-f79961.o

"_mxGetPr_800", referenced from:

_main in engdemo-f79961.o

ld: symbol(s) not found for architecture x86_64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

Ive read that I need to invoke a mex function, and I have downloaded one but dont know how to call it.