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The Hello pipeline

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Most of our training courses use a simple domain-agnostic pipeline to demonstrate Nextflow concepts and mechanisms. The Hello Nextflow course shows how to develop this pipeline in a step-by step way that explains every design and implementation decision. Other trainings use this pipeline, or parts of it, as a starting point.

This page summarizes the state of the pipeline as it stands at the completion of the Hello Nextflow course.

Summary description

The Hello workflow takes a CSV file containing greetings, writes them to separate files, converts each to uppercase, collects them back together again and outputs a single text file containing an ASCII picture of a fun character saying the greetings.

Workflow steps (processes)

The four steps are implemented as Nextflow processes (sayHello, convertToUpper, collectGreetings, and cowpy) stored in separate module files.

  1. sayHello: Writes each greeting to its own output file (e.g., "Hello-output.txt")
  2. convertToUpper: Converts each greeting to uppercase (e.g., "HELLO")
  3. collectGreetings: Collects all uppercase greetings into a single batch file
  4. cowpy: Generates ASCII art using the cowpy tool

Diagram

sayHello*-output.txtconvertToUpperUPPER-*collectGreetingsCOLLECTED-trio-output.txtHELLOBONJOURHOLàHello, English, 123 Bonjour, French, 456Holà, Spanish, 789greetings.csvHELLOBONJOURHOLàUPPER-Hello-output.txtUPPER-Bonjour-output.txtUPPER-Holà-output.txtcowPycowpy-COLLECTED-trio-output.txt--batch triotrio-report.txtThere were 3 greetingsin this batch.--input_________/ HOLà \| HELLO |\ BONJOUR /--------- \ ,+*^^*+___+++_ \ ,*^^^^ ) \ _+* ^**+_ \ +^ _ _++*+_+++_, ) _+^^*+_ ( ,+*^ ^ \+_ ) { ) ( ,( ,_+--+--, ^) ^\ { (\@) } f ,( ,+-^ __*_*_ ^^\_ ^\ ) {:;-/ (_+*-+^^^^^+*+*<_ _++_)_ ) ) / ( / ( ( ,___ ^*+_+* ) < < \ U _/ ) *--< ) ^\-----++__) ) ) ) ( ) _(^)^^)) ) )\^^^^^))^*+/ / / ( / (_))_^)) ) ) ))^^^^^))^^^)__/ +^^ ( ,/ (^))^)) ) ) ))^^^^^^^))^^) _) *+__+* (_))^) ) ) ))^^^^^^))^^^^^)____*^ \ \_)^)_)) ))^^^^^^^^^^))^^^^) (_ ^\__^^^^^^^^^^^^))^^^^^^^) ^\___ ^\__^^^^^^))^^^^^^^^)\\ ^^^^^\uuu/^^\uuu/^^^^\^\^\^\^\^\^\^\ ___) >____) >___ ^\_\_\_\_\_\_\) ^^^//\\_^^//\\_^ ^(\_\_\_\) ^^^ ^^ ^^^ ^

Results

The results are published to a directory called results/, and the final output of the pipeline (when run with default parameters) is a plain text file containing ASCII art of a turkey saying the uppercased greetings.

results/cowpy-COLLECTED-test-batch-output.txt
  _________
/ BONJOUR \
| HELLO   |
\ HOLà    /
---------
  \                                  ,+*^^*+___+++_
  \                           ,*^^^^              )
    \                       _+*                     ^**+_
    \                    +^       _ _++*+_+++_,         )
              _+^^*+_    (     ,+*^ ^          \+_        )
            {       )  (    ,(    ,_+--+--,      ^)      ^\
            { (\@)    } f   ,(  ,+-^ __*_*_  ^^\_   ^\       )
          {:;-/    (_+*-+^^^^^+*+*<_ _++_)_    )    )      /
          ( /  (    (        ,___    ^*+_+* )   <    <      \
          U _/     )    *--<  ) ^\-----++__)   )    )       )
            (      )  _(^)^^))  )  )\^^^^^))^*+/    /       /
          (      /  (_))_^)) )  )  ))^^^^^))^^^)__/     +^^
        (     ,/    (^))^))  )  ) ))^^^^^^^))^^)       _)
          *+__+*       (_))^)  ) ) ))^^^^^^))^^^^^)____*^
          \             \_)^)_)) ))^^^^^^^^^^))^^^^)
          (_             ^\__^^^^^^^^^^^^))^^^^^^^)
            ^\___            ^\__^^^^^^))^^^^^^^^)\\
                  ^^^^^\uuu/^^\uuu/^^^^\^\^\^\^\^\^\^\
                    ___) >____) >___   ^\_\_\_\_\_\_\)
                    ^^^//\\_^^//\\_^       ^(\_\_\_\)
                      ^^^ ^^ ^^^ ^

You may encounter some variations in the specifics depending on the course the pipeline is featured in.

Seqera

Seqera