bash (`dotnet`) and zsh (`_dotnet`) completion from https://docs.microsoft.com/en-us/dotnet/core/tools/enable-tab-autocomplete#bash

_dotnet

# zsh parameter completion for the dotnet CLI

_dotnet_zsh_complete()
{
  local completions=("$(dotnet complete "$words")")

  # If the completion list is empty, just continue with filename selection
  if [ -z "$completions" ]
  then
    _arguments '*::arguments: _normal'
    return
  fi

  # This is not a variable assignment, don't remove spaces!
  _values = "${(ps:\n:)completions}"
}

compdef _dotnet_zsh_complete dotnet

dotnet

# bash parameter completion for the dotnet CLI

_dotnet_bash_complete()
{
  local word=${COMP_WORDS[COMP_CWORD]}

  local completions
  completions="$(dotnet complete --position "${COMP_POINT}" "${COMP_LINE}" 2>/dev/null)"
  if [ $? -ne 0 ]; then
    completions=""
  fi

  COMPREPLY=( $(compgen -W "$completions" -- "$word") )
}

complete -f -F _dotnet_bash_complete dotnet