Establish sh as the default shell plugin.

This is a fix for one of the problems pointed out in #14176

lib/ansible/plugins/connection/__init__.py

@@ -83,7 +83,12 @@ class ConnectionBase(with_metaclass(ABCMeta, object)):
         elif hasattr(self, '_shell_type'):
             shell_type = getattr(self, '_shell_type')
         else:
-            shell_type = os.path.basename(C.DEFAULT_EXECUTABLE)
+            shell_type = 'sh'
+            shell_filename = os.path.basename(C.DEFAULT_EXECUTABLE)
+            for shell in shell_loader.all():
+                if shell_filename in shell.COMPATIBLE_SHELLS:
+                    shell_type = shell.SHELL_FAMILY
+                    break
 
         self._shell = shell_loader.get(shell_type)
         if not self._shell:

lib/ansible/plugins/shell/csh.py

@@ -21,6 +21,11 @@ from ansible.plugins.shell.sh import ShellModule as ShModule
 
 class ShellModule(ShModule):
 
+    # Common shell filenames that this plugin handles
+    COMPATIBLE_SHELLS = frozenset(('csh', 'tcsh'))
+    # Family of shells this has.  Must match the filename without extension
+    SHELL_FAMILY = 'csh'
+
     # How to end lines in a python script one-liner
     _SHELL_EMBEDDED_PY_EOL = '\\\n'
     _SHELL_REDIRECT_ALLNULL = '>& /dev/null'

lib/ansible/plugins/shell/fish.py

@@ -21,6 +21,11 @@ from ansible.plugins.shell.sh import ShellModule as ShModule
 
 class ShellModule(ShModule):
 
+    # Common shell filenames that this plugin handles
+    COMPATIBLE_SHELLS = frozenset(('fish',))
+    # Family of shells this has.  Must match the filename without extension
+    SHELL_FAMILY = 'fish'
+
     _SHELL_AND = '; and'
     _SHELL_OR = '; or'
     _SHELL_SUB_LEFT = '('

lib/ansible/plugins/shell/powershell.py

@@ -36,6 +36,13 @@ if _powershell_version:
 
 class ShellModule(object):
 
+    # Common shell filenames that this plugin handles
+    # Powershell is handled differently.  It's selected when winrm is the
+    # connection
+    COMPATIBLE_SHELLS = frozenset()
+    # Family of shells this has.  Must match the filename without extension
+    SHELL_FAMILY = 'powershell'
+
     def env_prefix(self, **kwargs):
         return ''
 

lib/ansible/plugins/shell/sh.py

@@ -30,6 +30,13 @@ _USER_HOME_PATH_RE = re.compile(r'^~[_.A-Za-z0-9][-_.A-Za-z0-9]*$')
 
 class ShellModule(object):
 
+    # Common shell filenames that this plugin handles.
+    # Note: sh is the default shell plugin so this plugin may also be selected
+    # if the filename is not listed in any Shell plugin.
+    COMPATIBLE_SHELLS = frozenset(('sh', 'zsh', 'bash', 'dash', 'ksh'))
+    # Family of shells this has.  Must match the filename without extension
+    SHELL_FAMILY = 'sh'
+
     # How to end lines in a python script one-liner
     _SHELL_EMBEDDED_PY_EOL = '\n'
     _SHELL_REDIRECT_ALLNULL = '> /dev/null 2>&1'