Dec 14, 2012

Nuke tcl tips

I have a lot of tcl expressions, and other nuke snippets written down, because always forget these. I decided to share some. In general I can say tcl in nuke is very flexible and quick for simple tasks.
For expression testing the expression I use the text node, easier than always getting into the specific knob, and click edit expression.
So first come the tcls in knob expressions, with examples:

Getting a knob's value of a specific node:
[value Read1.first]

Getting a knob's value of current node:
[value this.size]

Setting a knob's value of a specific node:
[knob Read1.first 10]

First frame of current read/write:
[value this.first_frame]

Setting a general tcl variable :
[set variablename value]
for example (tsize is the variable name):
[set tsize 15]

Using that variable later (notice the "$") for setting a knob value:
[knob this.size $tsize]

Name of the input node:

Expressions in a group going outside (to parentgroup or root). This example gives the name of the node before the group:

String substitute and compare:

Replace string in current node file knob with regex (string "proj" to "projects" in all occurences):
[regsub -all "proj" [value [node this].file] "projects"]

String map (replace multiple stringpairs):
[string map {"aa" "xx" "bb" "yy"} "aaffffaabb" ] this returns: xxffffxxyy

Compare values:
[string equal [value Text1.message] "bla"]

Regexp matching:
[regexp -inline "_v\[0-9]{3}" [value Read2.file]]

Path manipulations:

Filepath without extension:
[file rootname [value [topnode].file]]

Filename only:
[basename [value [topnode].file ]]

Filename only without extension:
[basename[file rootname [value [topnode].file]]]

This one splits the uppermost node's (probably a readnode) filepath by slashes and then joins together until a certain point, giving a directory few levels upper than the currrent path). "File split" does the splitting, making a list of directory names, "lrange ... 0 7 "selects a range from the list, from the beginning to the 7. item, and "join ... / " joins by forward slashes (which I use always in paths):

[join [lrange [file split [value [topnode].file]] 0 7] /]

This one can be used in a writenode fileknob to quickly convert the topmost readnode's path to another format(tga). Similar to the previous, but splits path by "." (different than previous file split), and gets the range from the beginning to 2 before the end, this way cutting off the extension and the counter (framecounter must have preceeded by a "." ) :

[join [lrange [split [value [topnode].file] .] 0 end-2] .].%04d.tga
(I use similar to make the comps writenode have the output path automatically getting from path of the nukescene )

Other useful:

Get the value the channel of a node, at a specific pixelcoordinates (e.g.: 10,10):
[sample [node input] red 10 10]

Setting a variable, without returning that (useful in a textnode):
[set seq [value Read1.file]; return]

Example of "IF" in an expression:
[if {condition} {expr1} else {expr2}]
for example:
[if {[value Switch1.which]==1} {return "aaa"} {return "bbb"}]

to be continued...


  1. Very nice document, it helps a lot, thank you very much!!

  2. what should be changes in autowrite node script if i want my output image name should be my read node input name...can u pls tell me the variables for read node....

  3. Thanks for these examples.. saved me time!

  4. Cool! How I do one simple loop of the animation?

    Example: When in frame 20, go to frame 1 ?

  5. please continue :)
    This is the absolute essence of what you need on a daily basis!