Assuming each command lies on a line of its own, read in one line at a time, then compare that string to every possible command that can be executed.
I don't know if this is the best way to do this. Should work though...
Code:
LineFromFile = ReadInOneLineFromAFile();

if(strcmp(LineFromFile, "Send_To_Origin") == 0)
{
   OutputToFile("G54_X0_Y0_Z0");
}
else if(strcmp(LineFromFile, "Rotate_90_Degrees") == 0)
{
   OutputToFile("G54_D90");
}
else if(...)
...

else
{
   OutputToConsole("Unknown command");
}