shell: Allow to configure history and init files path via env vars

Allow to customize the location of the shell history files via the
BEANQUERY_HISTORY environment variables. The environment variable name
has been chosen to resemble the ones used by sqlite3 and psql, but
with the BEANQUERY_ prefix.

Similarly, allow to customize the location of the init file via the
BEANQUERY_INIT environment variable.

Furthermore, respect the XGD_CONFIG_HOME environment variable when
determining the default location of these files.

Tilde expansion is performed on the values of all environment
variables: a leading path component equal to ~ is expanded to the
user's home directory location.

Fixes beancount#272.

Author: dnicolodi

beanquery/shell.py

@@ -41,8 +41,9 @@
     readline = None
 
 
-HISTORY_FILENAME = '~/.config/beanquery/history'
-INIT_FILENAME = '~/.config/beanquery/init'
+_HOME_CONFIG = os.environ.get('XDG_CONFIG_HOME', '~/.config')
+_HISTORY_FILENAME = path.expanduser(os.environ.get('BEANQUERY_HISTORY', path.join(_HOME_CONFIG, 'beanquery/history')))
+_INIT_FILENAME = path.expanduser(os.environ.get('BEANQUERY_INIT', path.join(_HOME_CONFIG, 'beanquery/init')))
 
 
 class style:
@@ -181,18 +182,17 @@ def __init__(self, outfile, interactive, runinit, settings):
             readline.set_completer_delims(" \t\n\"\\'`@$><=;|&{(")
 
             # Setup ``readline`` history handling.
-            history_filepath = path.expanduser(HISTORY_FILENAME)
-            os.makedirs(path.dirname(history_filepath), exist_ok=True)
+            os.makedirs(path.dirname(_HISTORY_FILENAME), exist_ok=True)
             with suppress(FileNotFoundError):
-                readline.read_history_file(history_filepath)
+                readline.read_history_file(_HISTORY_FILENAME)
                 readline.set_history_length(2048)
-            atexit.register(readline.write_history_file, history_filepath)
+            atexit.register(readline.write_history_file, _HISTORY_FILENAME)
 
         warnings.showwarning = self.warning
 
         if runinit:
             with suppress(FileNotFoundError):
-                with open(path.expanduser(INIT_FILENAME)) as f:
+                with open(_INIT_FILENAME) as f:
                     for line in f:
                         self.onecmd(line)