With Nextflow, you are not limited to Bash scripts -- you can use any scripting language! In other words, for each process you can use the language that best fits the specific task or that you simply prefer.
In the above example we define a simple pipeline with two processes.
The first process executes a Perl script, because the script block definition starts with a Perl shebang declaration (line 14). Since Perl uses the $ character for variables, we use the special shell block instead of the normal script block to easily distinguish the Perl variables from the Nextflow variables.
In the same way, the second process will execute a Python script, because the script block starts with a Python shebang (line 36).