I have a Read node for a plate in a Nuke script and would like to shift the inpoint to the first frame of my comp automatically. I tried cmd-dragging the value from my project Settings which gives me ‘:nuke:knob:knob.first_frame’ and results in an error.
What would be the correct expression for this?
That’s because the field in which you enter a frame number is not a number/value/integer; it’s a string (a word) which make what you are trying to do not work.
one easy way I use to have a customisable and quickly adaptable ‘start at’ frame is to use a ‘retime’ node. you only need to tick 2 boxes and then it will function as a nifty time offset.
there’s also the ‘time clip’ node which is specifically for these duties but it suffers the same problem as the read its self by having string fields instead of numbers/values.
set cut_paste_input [stack 0]
version 8.0 v4
push $cut_paste_input
Retime {
input.first_lock true
input.last 500
output.first 50
output.first_lock true
output.last 549
filter none
time ""
name Retime6
label "start frame: \[value output.first]"
selected true
xpos -7210
ypos -1530
}
use that as an example to make any clip start at f500 (I’d advise to set your reads up to ‘start at frame 1’ for this to work properly 
I’ve also made it print the value in the node too as an easy reference.
I may have misread what exactly you need to do but hope this will help anyway.
Rick