Source code to send instructions to the joints through the parallel port

Hi, where can i find the source code to send the instructions to the joints through the parallel port ?
Thanks a lot.

Thanks a lot andypugh!! Great Help!!
I am trying to instead of manually type the instructions (Commands + units to move each one of the axis) or read them from a file, to automatically receive that data from an other application written in C. So i should add in the CNC panel a button to select or deselect "automatic data transmission (Commands + units) towards the axis, that should switch from receiving the data through the textbox "Enter the MDI Commands" to a kind of transmission connection that automatically would receive the data. It would be of great help to find out, where is the code for the function of the "Go" button.
Thanks a lot for the help.

This maybe of help
linuxcnc.org/docs/html/man/man1/linuxcncrsh.1.html

This one may have you going through the docs
linuxcnc.org/docs/html/man/man1/linuxcncsvr.1.html

Thanks a lot, you are very valuable here. The best for you. I use my CNC also as a laser graver, and with the 6 motor steppers working I can make a arm robot of 6 degrees, that means 6 joints what it can in the entire space approaching any location in the space where is the object from any angle with the tool. It would be wonderful if there would be in the stepConf an option to select 6 labels XYZABC or XZYUVW. I don´t know why in the AXIS appears ABC, and where you configure the pins in UVW (step V, Dir V, etc). How do i should compile the source code copied from the GIT to my repository if I make a change (what compiler should i use) ? Many Thanks