better logging for "sh", 'runtime:shells' config key

example/kiwi.yml

@@ -6,6 +6,8 @@ version: '0.1'
 
 runtime:
   storage: /tmp/kiwi
+  shells:
+    - /bin/bash
   env: null
 
 markers:

src/kiwi/subcommands/sh.py

@@ -18,10 +18,38 @@ def _service_has_shell(config, args, compose_cmd, shell):
 
     except subprocess.CalledProcessError:
         # fallback
-        logging.info(f"Shell '{shell}' not found in container")
         return False
 
 
+def _find_shell(config, args, compose_cmd):
+    # as a last resort, fallback to "sh"
+    shells = ['/bin/sh', 'sh']
+
+    # load favorite shells from config
+    if config['runtime:shells']:
+        shells = [*config['runtime:shells'], *shells]
+
+    # consider shell from args
+    if args.shell:
+        shells = [args.shell, *shells]
+
+    logging.debug(f"Shells priority: {shells}")
+
+    # actually try shells
+    for i, shell in enumerate(shells):
+        if _service_has_shell(config, args, compose_cmd, shell):
+            # shell found
+            logging.debug(f"Using shell '{shell}'")
+            return shell
+        elif i + 1 < len(shells):
+            # not found, try next
+            logging.info(f"Shell '{shell}' not found in container, trying '{shells[i+1]}'")
+        else:
+            # not found, search exhausted
+            logging.error(f"None of the shells {shells} found in container, please provide -s SHELL!")
+            return None
+
+
 class ShCommand(ServiceCommand):
     def __init__(self):
         super().__init__(
@@ -31,22 +59,15 @@ class ShCommand(ServiceCommand):
 
         # -s switch: Select shell
         self._sub_parser.add_argument(
-            '-s', '--shell', type=str, default="/bin/bash",
+            '-s', '--shell', type=str,
             help="shell to spawn"
         )
 
     def run(self, config, args):
         compose_cmd = ['exec', args.services[0]]
-        shell = args.shell
-
-        if not _service_has_shell(config, args, compose_cmd, shell):
-            # fallback
-            shell = '/bin/bash'
-
-            if not _service_has_shell(config, args, compose_cmd, shell):
-                # safe fallback
-                shell = '/bin/sh'
+        shell = _find_shell(config, args, compose_cmd)
 
+        if shell:
             # spawn shell
             DockerCommand('docker-compose').run(
                 config, args, [*compose_cmd, shell]

src/kiwi_default.yml

@@ -1,6 +1,8 @@
 version:
 runtime:
   storage: /var/kiwi
+  shells:
+    - /bin/bash
   env: null
 markers:
   project: .project