Using the Command-line

This topic covers how to use the NUKE command line to execute Python scripts.

Running NUKE in Python Mode

NUKE can be executed in Python interpreter mode by using the -t argument. For example:

<Nuke-install-path>/Nuke13.0 -t
Nuke 13.0v1, 64 bit, built Mar  5 2021.
Copyright (c) 2021 The Foundry Visionmongers Ltd.  All Rights Reserved.
>>>

To execute a Python script at startup, use the script file name after the -t switch:

<Nuke-install-path>/Nuke13.0 -t <mypythonscript.py>

Using Command-line Arguments

When NUKE runs a Python script, it passes the script arguments to the script in sys.argv.

For example, first make a file called test.py containing the following:

import sys, nuke
print('sys.argv: {}'.format(sys.argv))

Now run this from the command line to see what sys.argv contains:

<Nuke-install-path>/Nuke13.0 -t test.py Hello World!
Nuke 13.0v1, 64 bit, built Mar  5 2021.
Copyright (c) 2021 The Foundry Visionmongers Ltd.  All Rights Reserved.
sys.argv: ['test.py', 'Hello', 'World!']

As you can see, NUKE passes the arguments after -t to the Python interpreter.

The only exception to this is if the last argument is a number or frame range. For example:

<Nuke-install-path>/Nuke13.0 -t test.py Hello World 1,2
WARNING: The command line argument ' 1,23' will be used as a Frame Range argument and will not be forward to the python sys.argv.
To define a frame range argument use the -F option.
Nuke 13.0v1, 64 bit, built Mar  5 2021.
Copyright (c) 2021 The Foundry Visionmongers Ltd.  All Rights Reserved.
sys.argv: ['test.py', 'Hello', 'World!']

In this case, the 1,20 is stripped from sys.args and the frame range is available in nuke.tcl(‘frames all’).

To access all the command-line arguments passed to nuke you can use:

nuke.rawArgs

For example, edit the test.py to contain the following:

import sys, nuke
print('sys.argv: {}'.format(sys.argv))
print('nuke.rawArgs: {}'.format(nuke.rawArgs))

Now execute this:

<Nuke-install-path>/Nuke13.0 -t test.py Hello World 1,2
WARNING: The command line argument ' 1,2' will be used as a Frame Range argument and will not be forward to the python sys.argv.
To define a frame range argument use the -F option.
Nuke 13.0v1, 64 bit, built Mar  5 2021.
Copyright (c) 2021 The Foundry Visionmongers Ltd.  All Rights Reserved.
sys.argv: ['test.py', 'Hello', 'World!']
nuke.rawArgs: ['./Nuke13.0', '-t', 'test.py', 'Hello', 'World!', '1,2']

Modifying Existing NUKE Scripts

It is sometimes useful to modify existing NUKE scripts using Python, for instance, when rewriting file paths.

The following script opens up a NUKE script on the command-line, rewrites all the write file paths, and finally saves the script:

### save this file as replaceWritePaths.py

import nuke
import os
import sys

def RecursiveFindNodes(nodeClass, startNode):
        if startNode.Class() == nodeClass:
                yield startNode
        elif isinstance(startNode, nuke.Group):
                for child in startNode.nodes():
                        for foundNode in RecursiveFindNodes(nodeClass, child):
                                yield foundNode



if len (sys.argv) != 5:
        print('Usage: NUKE replaceWritePaths.py <nuke_script> <new_nuke_script> <in_file_pattern> <new_file_pattern>')
        sys.exit(-1)

inScript = sys.argv[1]
outScript = sys.argv[2]
inPattern = sys.argv[3]
outPattern = sys.argv[4]

nuke.scriptOpen(inScript)

allWriteNodes = [w for w in RecursiveFindNodes('Write', nuke.root())]

for write in allWriteNodes:
        path = write['file'].value()
        path = path.replace(inPattern, outPattern)
        write['file'].setValue(path)

nuke.scriptSave(outScript)

This example has the following syntax when run:

./Nuke13.0 replaceWritePaths.py <nuke_script> <new_nuke_script> <in_file_pattern> <new_file_pattern>

Where:

<nuke_script> is the script to read in.
<new_nuke_script> is the name to save the modified script to.
<in_file_pattern> is string to search for in all the write file paths.
<new_file_pattern> is the string to replace <in_file_pattern> in all the write file paths.

Executing Frame Ranges

When running Python with the -t switch, NUKE does not render or execute any nodes by default.

To render a node you need to call:

nuke.execute(nodeName, firstFrame, lastFrame)

However, when you use the -x switch to render a frame range and you supply a Python file (.py) instead of a NUKE (.nk) script, NUKE executes the Python first and then renders all the writes in the script with the given frame range.

For example, save this script as convert.py:

import sys
import nuke
r = nuke.nodes.Read(file = sys.argv[1])
w = nuke.nodes.Write(file = sys.argv[2])
w.setInput(0, r)

Now, as an example, run the script from the command line as shown to convert some jpegs to tifs for 5 frames:

./Nuke13.0 -x convert.py myfiles.###.jpg myfiles.###.tif 1,5