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# 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:

    /Applications/Nuke6.3v1/Nuke6.3v1.app/Nuke6.3v1 -t

    NUKE 6.3v1, 64 bit, built Jul  4 2011.
    Copyright (c) 2011 The Foundry Visionmongers Ltd.  All Rights Reserved.
    Using "nukebeta" licence.
    >>>

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

    ./Nuke6.3v1 -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:

    ## make a file called test.py that contains the following

    import sys, nuke
    print sys.argv

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

    ./Nuke6.3v1 -t test.py Hello World

    NUKE 6.3v1, 64 bit, built Jul  4 2011.
    Copyright (c) 2011 The Foundry Visionmongers Ltd.  All Rights Reserved.
    Using "nukebeta" licence.
    ['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:

    ./Nuke6.3v1 -t test.py Hello World 1,20

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 nuke.rawArgs

Now execute this:

    ./Nuke6.3v1  -t test.py  Hello World 1,2

    NUKE 6.3v1, 64 bit, built Jul  4 2011.
    Copyright (c) 2011 The Foundry Visionmongers Ltd.  All Rights Reserved.
    Using "nukebeta" licence.
    ['/Applications/Nuke6.3v1b37/Nuke6.3v1b37.app/Nuke6.3v1b37', '-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:

    ./Nuke6.3v1 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:

    Nuke6.3v1 -x convert.py myfiles.###.jpg myfiles.###.tif 1,5

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