Nested brackets: the inner command runs first, its result feeds the outer one

[basename [value [topnode].file]]

Curly braces keep the text as it is: this returns the words [VALUE SIZE]

[string toupper {[value size]}]

Quotes let the brackets run: this returns the name of the node in capitals

[string toupper "[value name]"]

Value of a knob of this node (in its own label)

[value size]

Value of a knob of another node

[value Blur1.size]

One channel of a multi-value knob

[value Transform1.translate.x]
[value Grade1.white.r]

The literal content: an animated or linked knob shows its expression

[knob Transform1.rotate]

Set a knob (careful: in a label it runs every time the label is drawn)

[knob Transform1.translate.x 30]

Default value if the knob doesn't exist

[value this.missing_knob "n/a"]

This node, and its name

[value this.name]

The node connected to input 0, and to input 1

[value input.name]
[value input0.label]
[value input1.name]

Inside a group: the group itself, and the node connected to the group

[value parent.name]
[value this.parent.input.name]

The top node of the branch (usually the Read) and its file

[topnode]
[full_name [topnode]]
[value [topnode].file]

The project settings (Root): the path of the script, the fps, the frame range

[value root.name]
[value root.fps]
[value root.first_frame]-[value root.last_frame]

Does a node exist? (1 or 0)

[exists Read1]

Blur: size and filter

size: [value size]  [value filter]

Grade: the values that matter

gain: [value white]
gamma: [value gamma]

Transform: translate and rotate

t: [value translate.x], [value translate.y]
r: [value rotate]

Tracker or FrameHold: the reference frame

ref: [value reference_frame]
hold: [value first_frame]

Which channels the node works on, and the mix if it's not 1

[value channels]
[if {[value mix] != 1} {return "mix [value mix]"}]

Read node: just the file name, without folders

[file tail [value file]]

Switch: words instead of numbers

[if {[value which] == 0} {return "plate"} elseif {[value which] == 1} {return "CG"} else {return "other"}]

Show if the node is in error

[if {[value error]} {return "ERROR"}]

Script name, frame and date

[file rootname [file tail [value root.name]]]   frame [frame]   [date %d/%m/%Y]

The plate's file name and its frame range

[basename [value [topnode].file]]
[value [topnode].first]-[value [topnode].last]

Frame number with 4 digits (like 0012)

[format %04d [frame]]

A value with only 2 decimals

[format %.2f [value Transform1.rotate]]

Timecode from the plate's metadata

[metadata input/timecode]

Current frame

[frame]

Frame range of the script and of the Read

[value root.first_frame] - [value root.last_frame]
[value first_frame] - [value last_frame]

How many frames since the start of the plate

[expr {[frame] - [value [topnode].first]}]

Set a keyframe from TCL: knob, frame, value

[setkey Blur1.size 1001 10]

Width and height of the project and of the input

[value root.width] x [value root.height]
[value input.width] x [value input.height]

The format of the input (r = right = width, t = top = height)

[value input.format.r] x [value input.format.t]

Bounding box: left, bottom, right, top

[value bbox.x] [value bbox.y] [value bbox.r] [value bbox.t]

Centre of the format and centre of the bounding box (in an expression)

[value input.width]/2
([value bbox.x] + [value bbox.r]) / 2

Folder (/jobs/show/sh010/plates), file (sh010_plate_v003.1001.exr) and extension (.exr). Note: value gives the file name at the current frame, knob gives it with the padding (%04d or ####)

[file dirname [value [topnode].file]]
[file tail [value [topnode].file]]
[file extension [value [topnode].file]]

Without the extension, and the file name only

[file rootname [value [topnode].file]]
[basename [value [topnode].file]]
[basename [file rootname [value [topnode].file]]]

The folder of the Nuke script, to build relative paths

[file dirname [value root.name]]/renders/

Write node: name the render like the script, with the frame padding

[file dirname [value root.name]]/renders/[file rootname [file tail [value root.name]]].%04d.exr

Write node: same name as the top Read, in another format (cuts the frame number and the extension)

[join [lrange [split [value [topnode].file] .] 0 end-2] .].%04d.dpx

A folder some levels up: split the path, keep the first pieces, join them back

[join [lrange [file split [value [topnode].file]] 0 3] /]

The shot name, if it's the 3rd folder of the path

[lindex [split [value [topnode].file] /] 3]

The version of the script (v003)

[regexp -inline {v[0-9]+} [file tail [value root.name]]]

Upper case, lower case, length

[string toupper [value name]]
[string tolower [value name]]
[string length [value label]]

Part of a string: characters from 0 to 4, or the first character

[string range [value name] 0 4]
[string index [value name] 0]

Replace several words at once

[string map {"_v003" "_v004" "plates" "renders"} [value [topnode].file]]

Replace with a regular expression (every occurrence)

[regsub -all {v[0-9]+} [value [topnode].file] "v999"]

Compare two strings (1 if equal) and look for a word inside

[string equal [value Text1.message] "slate"]
[string match "*plate*" [value [topnode].file]]

Split a path by "/" and take an element

[lindex [split [value [topnode].file] /] end]
[lindex [split [value [topnode].file] /] end-1]

How many pieces, and a range of them

[llength [split [value [topnode].file] /]]
[lrange [split [file tail [value [topnode].file]] _] 0 1]

Join a list back with a separator

[join [lrange [split [file tail [value [topnode].file]] _] 0 1] _]

Sort, search, replace an element

[lsort [split "c b a" " "]]
[lsearch [split [value [topnode].file] /] plates]
[lreplace [split [value [topnode].file] /] 4 4 renders]

if / elseif / else

[if {[value size] > 10} {return "big blur"} else {return "small blur"}]

Compare strings in a condition (use eq for text)

[if {[value filter] eq "gaussian"} {return "G"} {return "other"}]

Maths with expr (always in braces)

[expr {[value size] * 2}]
[expr {round([value Transform1.rotate])}]
[expr {[frame] % 2}]

Read a pixel: node, channel, x, y

[sample [node input] red 960 540]

Read the pixel under a position knob (here the center of Transform1)

[sample [node input] red [value Transform1.center.x] [value Transform1.center.y]]

Metadata of the input

[metadata input/filename]
[metadata input/timecode]

Save a value in a variable without printing it (end with return)

[set plate [basename [value [topnode].file]]; return]
plate: $plate

Set a knob of another node

[knob Read1.first 1001]

Python inside TCL: [python ...], with braces when there are spaces

[python nuke.thisNode().name()]
[python {nuke.script_directory()}]/render.exr

An environment variable (through Python)

[python {__import__("os").getenv("SHOT", "no shot")}]

TCL inside Python: nuke.tcl() returns the result as a string

name = nuke.tcl("value root.name")
nuke.tcl("knob Blur1.size 5")
print(nuke.tcl("basename [value Read1.file]"))

Value of a knob at another frame: one frame before, a fixed frame

Transform1.translate.x(frame - 1)
Tracker1.translate.x(1001)

Offset an animation by 50 frames

Transform1.translate.x(frame + 50)

Condition: condition ? then : else

frame < 1050 ? 0 : 1

Wiggle, noise and waves

random(frame) * 10
noise(frame / 10) * 20
sin(frame / 5) * 30

Link to the parent group's knob

parent.size

Backdrop or StickyNote: the name of the shot from the script name (sh010_comp_v003.nk becomes sh010)

[lindex [split [file tail [value root.name]] _] 0]

Slate line for dailies

[lindex [split [file tail [value root.name]] _] 0]  |  [regexp -inline {v[0-9]+} [file tail [value root.name]]]  |  frame [format %04d [frame]]  |  [date %d/%m/%Y]

Read node label: file name and frame range at a glance

[file tail [knob file]]
[value first]-[value last]

Write node: version taken from the script name

[file dirname [value root.name]]/renders/[file rootname [file tail [value root.name]]]/[file rootname [file tail [value root.name]]].%04d.exr

Blur that shows its size and filter

Blur {
 size 10
 name Blur_labelled
 label "size \[value size]  \[value filter]"
}

Grade that shows gain and gamma

Grade {
 name Grade_labelled
 label "gain \[value white]\ngamma \[value gamma]"
}

Switch that says plate or CG

Switch {
 name Switch_labelled
 label "\[if {\[value which] == 0} {return plate} {return CG}]"
}

Text node burn-in: shot, script name and frame

Text2 {
 message "\[lindex \[split \[file tail \[value root.name]] _] 0]   \[file rootname \[file tail \[value root.name]]]   frame \[format %04d \[frame]]"
 name Slate_burnin
}

Write node that names the render after the script, in a renders folder next to it

Write {
 file "\[file dirname \[value root.name]]/renders/\[file rootname \[file tail \[value root.name]]]/\[file rootname \[file tail \[value root.name]]].####.exr"
 file_type exr
 name Write_auto
}

Backdrop with the shot name taken from the script name

BackdropNode {
 inputs 0
 name Backdrop_shot
 label "\[lindex \[split \[file tail \[value root.name]] _] 0]"
 note_font_size 42
 bdwidth 420
 bdheight 300
}