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 1. Select "Terminal->New terminal"
12 2. Create a new git repository to hold our workflow with this command:
15 git init rnaseq-cwl-training-exercises
21 git clone https://github.com/arvados/arvados-vscode-cwl-template.git rnaseq-cwl-training-exercises
24 3. Go to File->Open Folder and select rnaseq-cwl-training-exercises
26 4. Go to the terminal window
28 5. Import bio-cwl-tools with this command:
31 git submodule add https://github.com/common-workflow-library/bio-cwl-tools.git
34 ## Writing the workflow
38 Create a new file "main.cwl"
40 Start with this header.
46 label: RNAseq CWL practice workflow
49 ### 2. Workflow Inputs
51 The purpose of a workflow is to consume some input parameters, run a
52 series of steps, and produce output values.
54 For this analysis, the input parameters are the fastq file and the reference data required by STAR.
56 In the original shell script, the following variables are declared:
59 # initialize a variable with an intuitive name to store the name of the input fastq file
62 # directory with genome reference FASTA and index files + name of the gene annotation file
63 genome=rnaseq/reference_data
64 gtf=rnaseq/reference_data/chr1-hg19_genes.gtf
67 In CWL, we will declare these variables in the `inputs` section.
69 The inputs section lists each input parameter and its type. Valid
70 types include `File`, `Directory`, `string`, `boolean`, `int`, and
73 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:
84 A workflow consists of one or more steps. This is the `steps` section.
86 Now we need to describe the first step of the workflow. This step is to run `fastqc`.
88 A workflow step consists of the name of the step, the tool to `run`,
89 the input parameters to be passed to the tool in `in`, and the output
90 parameters expected from the tool in `out`.
92 The value of `run` references the tool file. Tip: while typing the
93 file name, you can get suggestions and auto-completion on a partial
94 name using control+space.
96 The `in` block lists input parameters to the tool and the workflow
97 parameters that will be assigned to those inputs.
99 The `out` block lists output parameters to the tool that are used
100 later in the workflow.
102 You need to know which input and output parameters are available for
103 each tool. In vscode, click on the value of `run` and select "Go to
104 definition" to open the tool file. Look for the `inputs` and
105 `outputs` sections of the tool file to find out what parameters are
111 run: bio-cwl-tools/fastqc/fastqc_2.cwl
117 ### 4. Running alignment with STAR
119 STAR has more parameters. Sometimes we want to provide input values
120 to a step without making them as workflow-level inputs. We can do
121 this with `{default: N}`
129 run: bio-cwl-tools/STAR/STAR-Align.cwl
131 RunThreadN: {default: 4}
134 OutSAMtype: {default: BAM}
135 OutSAMunmapped: {default: Within}
139 ### 5. Running samtools
141 The third step is to generate an index for the aligned BAM.
143 For this step, we need to use the output of a previous step as input
144 to this step. We refer the output of a step by with name of the step
145 (STAR), a slash, and the name of the output parameter (alignment), e.g. `STAR/alignment`
147 This creates a dependency between steps. This means the `samtools`
148 step will not run until the `STAR` step has completed successfully.
152 run: bio-cwl-tools/samtools/samtools_index.cwl
154 bam_sorted: STAR/alignment
155 out: [bam_sorted_indexed]
160 As of this writing, the `subread` package that provides
161 `featureCounts` is not available in bio-cwl-tools (and if it has been
162 added since writing this, let's pretend that it isn't there.) We will
163 dive into how to write a CWL wrapper for a command line tool in
164 lesson 2. For now, we will leave off the final step.
166 ### 7. Workflow Outputs
168 The last thing to do is declare the workflow outputs in the `outputs` section.
170 For each output, we need to declare the type of output, and what
171 parameter has the output value.
173 Output types are the same as input types, valid types include `File`,
174 `Directory`, `string`, `boolean`, `int`, and `float`.
176 The `outputSource` field refers the a step output in the same way that
177 the `in` block does, the name of the step, a slash, and the name of
178 the output parameter.
180 For our final outputs, we want the results from fastqc and the
181 aligned, sorted and indexed BAM file.
187 outputSource: fastqc/html_file
190 outputSource: samtools/bam_sorted_indexed