make Rscript a variable and re-use

pre_commit/languages/r.py

@@ -18,6 +18,7 @@
 from pre_commit.util import win_exe
 
 ENVIRONMENT_DIR = 'renv'
+RSCRIPT_PROGRAM = 'Rscript'
 RSCRIPT_OPTS = ('--no-save', '--no-restore', '--no-site-file', '--no-environ')
 get_default_version = helpers.basic_get_default_version
 health_check = helpers.basic_health_check
@@ -61,7 +62,7 @@ def _prefix_if_non_local_file_entry(
 
 def _rscript_exec() -> str:
     r_home = os.environ.get('R_HOME')
-    program = win_exe('Rscript')
+    program = win_exe(RSCRIPT_PROGRAM)
     if r_home is None:
         return program
     else:
@@ -74,16 +75,16 @@ def _entry_validate(entry: Sequence[str]) -> None:
     # Rscript -e expr
     # Rscript path/to/file
     """
-    if entry[0] != 'Rscript':
-        raise ValueError('entry must start with `Rscript`.')
+    if entry[0] != RSCRIPT_PROGRAM:
+        raise ValueError(f'entry must start with `{RSCRIPT_PROGRAM}`.')
 
     if entry[1] == '-e':
         if len(entry) > 3:
             raise ValueError('You can supply at most one expression.')
     elif len(entry) > 2:
         raise ValueError(
-            'The only valid syntax is `Rscript -e {expr}`',
-            'or `Rscript path/to/hook/script`',
+            f'The only valid syntax is `{RSCRIPT_PROGRAM} -e {{expr}}`',
+            f'or `{RSCRIPT_PROGRAM} path/to/hook/script`',
         )