1 # Turning a shell script into a workflow using existing tools
3 In this lesson we will turn `rnaseq_analysis_on_input_file.sh` into a workflow.
7 We will create a new git repository and import a library of existing
8 tool definitions that will help us build our workflow.
10 Create a new git repository to hold our workflow with this command:
13 git init rnaseq-cwl-training-exercises
19 git clone https://github.com/arvados/arvados-vscode-cwl-template.git rnaseq-cwl-training-exercises
22 Next, import bio-cwl-tools with this command:
25 git submodule add https://github.com/common-workflow-library/bio-cwl-tools.git
28 ## Writing the workflow
32 Create a new file "main.cwl"
34 Start with this header.
40 label: RNAseq CWL practice workflow
43 ### 2. Workflow Inputs
45 The purpose of a workflow is to consume some input parameters, run a
46 series of steps, and produce output values.
48 For this analysis, the input parameters are the fastq file and the reference data required by STAR.
50 In the original shell script, the following variables are declared:
53 # initialize a variable with an intuitive name to store the name of the input fastq file
56 # directory with genome reference FASTA and index files + name of the gene annotation file
57 genome=rnaseq/reference_data
58 gtf=rnaseq/reference_data/chr1-hg19_genes.gtf
61 In CWL, we will declare these variables in the `inputs` section.
63 The inputs section lists each input parameter and its type. Valid
64 types include `File`, `Directory`, `string`, `boolean`, `int`, and
67 In this case, the fastq and gene annotation file are individual files. The STAR index is a directory. We can describe these inputs in CWL like this:
78 A workflow consists of one or more steps. This is the `steps` section.
80 Now we need to describe the first step of the workflow. This step is to run `fastqc`.
82 A workflow step consists of the name of the step, the tool to `run`,
83 the input parameters to be passed to the tool in `in`, and the output
84 parameters expected from the tool in `out`.
86 The value of `run` references the tool file. Tip: while typing the
87 file name, you can get suggestions and auto-completion on a partial
88 name using control+space.
90 The `in` block lists input parameters to the tool and the workflow
91 parameters that will be assigned to those inputs.
93 The `out` block lists output parameters to the tool that are used
94 later in the workflow.
96 You need to know which input and output parameters are available for
97 each tool. In vscode, click on the value of `run` and select "Go to
98 definition" to open the tool file. Look for the `inputs` and
99 `outputs` sections of the tool file to find out what parameters are
105 run: bio-cwl-tools/fastqc/fastqc_2.cwl
111 ### 4. Running alignment with STAR
113 STAR has more parameters. Sometimes we want to provide input values
114 to a step without making them as workflow-level inputs. We can do
115 this with `{default: N}`
123 run: bio-cwl-tools/STAR/STAR-Align.cwl
125 RunThreadN: {default: 4}
128 OutSAMtype: {default: BAM}
129 OutSAMunmapped: {default: Within}
133 ### 5. Running samtools
135 The third step is to generate an index for the aligned BAM.
137 For this step, we need to use the output of a previous step as input
138 to this step. We refer the output of a step by with name of the step
139 (STAR), a slash, and the name of the output parameter (alignment), e.g. `STAR/alignment`
141 This creates a dependency between steps. This means the `samtools`
142 step will not run until the `STAR` step has completed successfully.
146 run: bio-cwl-tools/samtools/samtools_index.cwl
148 bam_sorted: STAR/alignment
149 out: [bam_sorted_indexed]
154 As of this writing, the `subread` package that provides
155 `featureCounts` is not available in bio-cwl-tools (and if it has been
156 added since writing this, let's pretend that it isn't there.) We will
157 dive into how to write a CWL wrapper for a command line tool in
158 lesson 2. For now, we will leave off the final step.
160 ### 7. Workflow Outputs
162 The last thing to do is declare the workflow outputs in the `outputs` section.
164 For each output, we need to declare the type of output, and what
165 parameter has the output value.
167 Output types are the same as input types, valid types include `File`,
168 `Directory`, `string`, `boolean`, `int`, and `float`.
170 The `outputSource` field refers the a step output in the same way that
171 the `in` block does, the name of the step, a slash, and the name of
172 the output parameter.
174 For our final outputs, we want the results from fastqc and the
175 aligned, sorted and indexed BAM file.
181 outputSource: fastqc/html_file
184 outputSource: samtools/bam_sorted_indexed