Fixes suggested by @mirpedrol during review. Thanks!

README.md

@@ -20,8 +20,7 @@ A python package with helper tools for the nf-core community.
 - [`nf-core` tools update](#update-tools)
 - [`nf-core list` - List available pipelines](#listing-pipelines)
 - [`nf-core launch` - Run a pipeline with interactive parameter prompts](#launch-a-pipeline)
-- [`nf-core download` - Download pipeline for offline use](#downloading-pipelines-for-offline-use)
-- [`nf-core download --tower` - Adapting downloads to Nextflow Tower](#adapting-downloads-to-nextflow-tower)
+- [`nf-core download` - Download a pipeline for offline use](#downloading-pipelines-for-offline-use)
 - [`nf-core licences` - List software licences in a pipeline](#pipeline-software-licences)
 - [`nf-core create` - Create a new pipeline with the nf-core template](#creating-a-new-pipeline)
 - [`nf-core lint` - Check pipeline code against nf-core guidelines](#linting-a-workflow)

nf_core/download.py

@@ -423,13 +423,13 @@ def prompt_singularity_cachedir_creation(self):
                     ToDo: "sh", "dash", "ash","csh", "tcsh", "ksh", "fish", "cmd", "powershell", "pwsh"?
                     """
 
-                    if os.environ["SHELL"] == "/bin/bash":
+                    if os.getenv("SHELL", "") == "/bin/bash":
                         shellprofile_path = os.path.expanduser("~/~/.bash_profile")
                         if not os.path.isfile(shellprofile_path):
                             shellprofile_path = os.path.expanduser("~/.bashrc")
                             if not os.path.isfile(shellprofile_path):
                                 shellprofile_path = False
-                    elif os.environ["SHELL"] == "/bin/zsh":
+                    elif os.getenv("SHELL", "") == "/bin/zsh":
                         shellprofile_path = os.path.expanduser("~/.zprofile")
                         if not os.path.isfile(shellprofile_path):
                             shellprofile_path = os.path.expanduser("~/.zshenv")