Step 15 - Make output files/paths unique

Let us describe a way to avoid the above issue. There are other approaches to resolve this issue, but let us for the moment look at one that can easily be reused.

// Step - 15
process process_step15 {
    publishDir "output/${config.id}"
    input:
        tuple val(id), file(input), val(config)
    output:
        tuple val("${id}"), file("output.txt"), val("${config}")
    script:
        """
        a=`cat $input`
        let result="\$a + ${config.term}"
        echo "\$result" > output.txt
        """
}
workflow step15 {
    Channel.fromPath( params.input ) \
        | map{ el ->
            [
              el.baseName,
              el,
              [
                "id": el.baseName,
                "operator" : "-",
                "term" : 10
              ]
            ] } \
        | process_step15 \
        | view{ [ it[0], it[1] ] }
}

This results in the following:

> nextflow -q run . -entry step15 --input "data/input?.txt"
WARN: DSL 2 IS AN EXPERIMENTAL FEATURE UNDER DEVELOPMENT -- SYNTAX MAY CHANGE IN FUTURE RELEASE
[input3, <...>/work/a1/0947168c069ee6f4e1e7a850f268ea/output.txt]
[input1, <...>/work/d2/41f7e0ec2fb3f8e4204aca6bf952ab/output.txt]
[input2, <...>/work/f5/845a17a4e548c531b7c63a06e50304/output.txt]

With the following result:

> cat output/input?/output.txt
11
12
13

In other words, since (in this case 3) parallel branches each write to the same output location we have to make sure that we add something unique for every of the parallel branches. Another approach is to tweak the name of the output file in the process, but for the moment it is still fixed and defined in the process itself. Let us take a look at that aspect next.