Running the JWST pipeline: Command Line Interface (strun)


For seasoned users who are familiar with using collect_pipeline_cfgs and running pipelines by the default configuration (CFG) files, please note that this functionality has been deprecated. Please read CFG Usage Deprecation Notice.

Individual steps and pipelines (consisting of a series of steps) can be run and configured from the command line using the strun command. strun is one of two options for running the pipeline. See here for an overview of the alternative Python interface.

CRDS Environment Variables

The CRDS environment variables need to be defined before running a pipeline or step with strun to allow the pipeline to access reference and parameter files. See CRDS for more information.

Overview of Running the Pipeline with strun

The first argument to strun must be one of either a pipeline name, Python class of the step or pipeline to be run, or the name of a parameter file for the desired step or pipeline (see Parameter Files). The second argument to strun is the name of the input data file to be processed.

$ strun <pipeline_name, class_name, or parameter_file> <input_file>

Pipeline classes also have a pipeline name, or alias, that can be used instead of the full class specification. For example, jwst.pipeline.Detector1Pipeline has the alias calwebb_detector1 and can be run as

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

A full list of pipeline aliases can be found in Pipeline Stages.

Exit Status

strun produces the following exit status codes:

  • 0: Successful completion of the step/pipeline

  • 1: General error occurred

  • 64: No science data found

The “No science data found” condition is returned by the assign_wcs step of the calwebb_spec2 pipeline when, after successfully determining the WCS solution for a file, the WCS indicates that no science data will be found. This condition most often occurs with NIRSpec’s Multi-object Spectroscopy (MOS) mode: There are certain optical and MSA configurations in which dispersion will not cross one or the other of NIRSpec’s detectors.

Configuring a Pipeline/Step with strun

By default, pipeline parameters and reference files are chosen by CRDS based on instrument, observing mode, date, etc. If set to the most current Reference Files Mappings (CRDS Context), these represent the ‘best’ set of parameters and reference files for the pipeline as determined by the JWST instrument teams.

A Pipeline/Step can be configured for custom processing. Pipeline-level and step-level parameters can be changed, output file behavior can be set, references files can be overridden, and pipeline steps can be skipped if desired. This section will be a general overview on how to configure the pipeline when running with strun, and the following sections will elaborate on each of these possible customizations and demonstrate usage.

When running command line with ``strun``, there are two ways two configure a Pipeline/Step.

  1. By passing in arguments to a pipeline/step on the command line

  2. By using a parameter file and passing this in as an argument on the command line

A combination of arguments and custom parameter files can be used for configuration, but keep in mind the hierarchy of parameter precedence to keep track of which value will get used if set in multiple locations.

Setting Step Parameters on a Pipeline or Individual Step

All pipelines and steps have parameters that can be set to change various aspects of how they execute (e.g switching on and off certain options in a step, setting thresholds). By default, the values of these parameters are set in the CRDS-chosen parameter file, but they can be overridden when running the pipeline with strun. As mentioned, this can either be done by passing in command line arguments or by passing in a custom parameter file - both methods will be described in this section.

Using Command Line Arguments

When running a pipeline, step-level parameters can be changed by passing in a command line argument to that step. For example, to change the rejection_threshold parameter of the jump detection step when running the full Detector1Pipeline:

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

When running a standalone step, command line arguments do not need to be nested within steps. For example, to change the parameter rejection_threshold for the jump detection step when running the step individually:

$ strun jump jw00017001001_01101_00001_nrca1_uncal.fits --rejection_threshold=12.0

Using a Parameter File

Alternatively, if using a parameter file, edit the file to add the following snippet (in this example, to a file named ‘my_config_file.asdf’ in the current working directory):

- class: jwst.jump.jump_step.JumpStep
  name: jump
    rejection_threshold : 12

And pass in the modified file to strun:

$ strun my_config_file.asdf jw00017001001_01101_00001_nrca1_uncal.fits

Overriding Reference Files

By default, when the pipeline or step is run, CRDS will determine the best set of reference files based on file metadata and the current CRDS mapping (also known as ‘context’). It is possible to override these files and use a custom reference file, or one not chosen by CRDS.

Using Command Line Arguments

For any step that uses a calibration reference file you always have the option to override the automatic selection of a reference file from CRDS and specify your own file to use. Parameters for this are of the form --override_<ref_type>, where ref_type is the name of the reference file type, such as mask, dark, gain, or linearity. When in doubt as to the correct name, just use the -h argument to strun to show you the list of available override parameters.

To override the use of the default linearity reference file selection with a custom file in the current working directory called my_lin.fits, for example, you would do:

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

Or, if running the step individually, to override the reference file:

$ strun linearity jw00017001001_01101_00001_nrca1_uncal.fits

Using a Parameter File

If using a parameter file for configuration, to override a reference edit the file to add the following snippet (in this example, to a file named ‘my_config_file.asdf’ in the current working directory):

- class: jwst.saturation.saturation_step.SaturationStep
  name: saturation
    override_saturation: '/path/to/new_saturation_ref_file.fits'

And pass in the modified file to strun:

$ strun my_config_file.asdf jw00017001001_01101_00001_nrca1_uncal.fits

To use an entire set of past reference files from a previous CRDS mapping, see here.

Skipping a Pipeline Step


Some steps in a pipeline expect certain previous steps to have been run beforehand, and therefore won’t run if that expected previous correction has not been applied. Proceed with caution when skipping steps.

When running a pipeline with strun, one or several steps within that pipeline can be skipped.

Using Command Line Arguments

Every step in a pipeline has a skip parameter that when set to true, will entirely skip that step. For example, to skip the saturation step in the Detector1Pipeline:

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

Using a Parameter File

The equivalent to the above example can be done by adding the following snippet to your parameter file (in this example, to a file named ‘my_config_file.asdf’ in the current working directory):

- class: jwst.saturation.saturation_step.SaturationStep
    skip: true

And pass in the modified file to the config_file argument:

result ='jw00017001001_01101_00001_nrca1_uncal.fits',

Controlling Output File Behavior with strun

By default, when running the pipeline with strun, the final outputs of a pipeline (or final outputs when running an individual step) will be written out to a file in the current working directory. The base name of these final output files is derived from the input file name, by default. Additionally, no intermediate step results will be saved. This behavior can be modified to change output file names, locations, and specify that intermediate results from a step in a pipeline should be written out to a file.

Saving Intermediate Pipeline Results to a File

The stpipe infrastructure automatically passes the output data model from one step to the input of the next step, without saving any intermediate results to disk. If you want to save the results from individual steps, you have two options:

  • Specify save_results on an individual step within the pipeline. This option will save the results of the step, using a filename created by the step.

  • Specify a file name using output_file <basename> for an individual step. This option indicated that results should be saved, and to use the name specified.

For example, to save the result from the dark current step of Detector1Pipeline (using the alias name calwebb_detector1):

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

This will create the file jw00017001001_01101_00001_dark_current.fits in the current working directory.

Setting Output File Name

As demonstrated in the section above, the output_file parameter is used to specify the desired name for output files. When done at the step-level as shown in those examples, the intermediate output files from steps within a pipeline are saved with the specified name.

You can also specify a particular file name for saving the end result of the entire pipeline using the --output_file parameter:

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

In this situation, using the default configuration, three files are created:

  • stage1_processed_trapsfilled.fits

  • stage1_processed_rate.fits

  • stage1_processed_rateints.fits

When running a standalone step, setting --output_file at the top-level will determine the name of the final output product for that step, overriding the default based on input name:

$ strun linearity jw00017001001_01101_00001_nrca1_uncal.fits

Similarly, to save the result from a step within a pipeline (for example, the dark current step of calwebb_detector1) with a different file name:

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

A file, intermediate_result_dark_current.fits, will then be created. Note that the name of the step will be appended as the file name suffix

Setting Output File Directory

To change the output directory of the final pipeline products from the default of the current working directory, use the output_dir option.

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

When this is run, all three final output products of Detector1Pipeline will be saved within the subdirectory calibrated.

Setting output_dir at the step-level indicates that the step’s result should be saved (so, also setting save_results is redundant), and that the files should be saved in the directory specified instead of the current working directory. For example, to save the intermediate results of DarkCurrentStep when running Detector1Pipeline in a subdirectory /calibrated:

$ strun calwebb_detector1 jw00017001001_01101_00001_nrca1_uncal.fits

Similarly, when output_dir is set on an individual step class, this will indicate that the result from that step should be saved to the specified directory:

$ strun dark_current jw00017001001_01101_00001_nrca1_uncal.fits --output_dir='calibrated'