class_docstr: General support for FreeSurfer commands.
  
  Every FS command accepts 'subjects_dir' input.
class_docstr_tok: ["General","support","for","FreeSurfer","commands",".","Every","FS","command","accepts","'subjects_dir","'","input","."]
code: def _subjects_dir_update(self):
      if self.inputs.subjects_dir:
          self.inputs.environ.update(
              {"SUBJECTS_DIR": self.inputs.subjects_dir}
          )
  
imports: import os
  from looseversion import LooseVersion
  from ...utils.filemanip import fname_presuffix
  from ..base import CommandLine, Directory, CommandLineInputSpec, isdefined, traits, TraitedSpec, File, PackageInfo
label_desc: Use image node_id 2 for calling the FSCommand obj's underlying member method code with example usage: obj._subjects_dir_update() without return types