Add a Shell class

poetry/utils/shell.py

+import os
+
+from shellingham import detect_shell
+from shellingham import ShellDetectionFailure
+
+
+class Shell:
+    """
+    Represents the current shell.
+    """
+
+    _shell = None
+
+    def __init__(self, name, path):  # type: (str, str) -> None
+        self._name = name
+        self._path = path
+
+    @property
+    def name(self):  # type: () -> str
+        return self._name
+
+    @property
+    def path(self):  # type: () -> str
+        return self._path
+
+    @classmethod
+    def get(cls):  # type: () -> Shell
+        """
+        Retrieve the current shell.
+        """
+        if cls._shell is not None:
+            return cls._shell
+
+        try:
+            name, path = detect_shell(os.getpid())
+        except (RuntimeError, ShellDetectionFailure):
+            raise RuntimeError("Unable to detect the current shell.")
+
+        cls._shell = cls(name, path)
+
+        return cls._shell
+
+    def __repr__(self):  # type: () -> str
+        return '{}("{}", "{}")'.format(self.__class__.__name__, self._name, self._path)

pyproject.toml

@@ -34,6 +34,7 @@ pyparsing = "^2.2"
 cachecontrol = { version = "^0.12.4", extras = ["filecache"] }
 pkginfo = "^1.4"
 html5lib = "^1.0"
+shellingham = "^1.1"
 
 # The typing module is not in the stdlib in Python 2.7 and 3.4
 typing = { version = "^3.6", python = "~2.7 || ~3.4" }