code: def get_r_command():
      if "NIPYPE_NO_R" in os.environ:
          return None
      r_cmd = os.getenv("RCMD", default="R")
  
      return r_cmd if which(r_cmd) else None
  
file_path: nipype/nipype/interfaces/r.py
imports: import os
  from shutil import which
  from ..None import config
  from .base import CommandLineInputSpec, InputMultiPath, isdefined, CommandLine, traits, File, Directory
label_desc: Use image node_id 1 for calling a global function with example usage: get_r_command() and returns: unknown, None