$ wget https://prdownloads.sourceforge.net/tcl/tcl8.6.10-src.tar.gz
$ tar xvf tcl8.6.10-src.tar.gz 
$ cd tcl8.6.10/unix
$ mkdir build
$ cd build
$ ../configure --prefix=/opt/tcl/8.6.10 --enable-threads --enable-shared 
$ make
$ make install