How to Control a PWM Gripper

I have my hobby robot gripper working and an Axis GUI slider to manually control/test it.  So now I need a hook to control the gripper from an eventual gcode program.

I'm thinking of having 3 states, Open, Close, Variable.  I'll need to output a float value, so is this best suited for G, M, O, or other code? 

Secondly are "aliases" possible in gcode?  For example "Gripper Open"  or "M65 Open" something relatively simple.

You could use the 'motion.analog-out' pins (M68):
linuxcnc.org/docs/html/gcode/m-code.html#mcode:m68

If you wanted you could define your own M-code or Subroutine that sets a particular analog output pin so you would not have to enter the E-word all the time.

We cannot pass strings in gcode and the only way to use something like that would be a subroutine (eg o<yoursubroutine>call)

I'm thinking about readability, so is this possible with subroutines...

Open CALL
Close CALL
Open 50 CALL (representing 50% full scale)

No that is not possible, subroutine calls need to use the 'O' Word (O <your_subroutine> CALL)
Note: lowercase lettering is also fine like in my last post. Subroutines can also accept parameter values (O <your_subroutine> CALL [123] [456] ...)
Remapped Mcodes can also pass P and Q words: (M456 P1 Q2)

Has anyone been able to use M codes to operate a Robotic Arm gripper yet? I have a post for a Scorbot-ER-3 and Linuxcnc 2.9.1 which uses a gui and mouse to open and close the gripper, but need to make a M code for this function. Please help

Please a few questions.
I have a Scorbot-ER-3 (with original control box) working using LinuxCNC, But cannot activate the gripper using G-Code commands or the Logitech dual action F310 controller pendant. When Andy designed this for LinuxCNC in 2020 the only way to open or close the grippers is through a GUI pop-up box and the mouse.
Thank you for your time.

i use M68 to control my rc-servo gripper's
so i can control it by gcode and for the gui i use mdi commands and a vcp gui with buttons to set some fixed positions

[HALUI]
MDI_COMMAND = M68 E0 Q-100
MDI_COMMAND = M68 E0 Q-75
MDI_COMMAND = M68 E0 Q0
MDI_COMMAND = M68 E0 Q75
MDI_COMMAND = M68 E0 Q100

www.youtube.com/shorts/Tp3savo-MGs

Please do you have any more details on this?
How do you use the M68 to open?
How do you use the M68 to close?
Do you have M68 (number value)?

www.linuxcnc.org/docs/html/gcode/m-code.html#mcode:m68

See the note about the hal pin.

Looks like meister was using different numbers for different positions
some likely being fully open and some fully closed

exactly, the servo is configured as an analog output and can be controlled with values from -100 (open) to +100(closed).