[pr6953-docs] update docstrings/whatsnew/shell.rst for env/set_env magic

docs/source/whatsnew/pr/env_magic.md

@@ -0,0 +1,1 b''
+* Enhanced support for `env` magic.  As before, `env` with no arguments displays all environment variables and values.  Additionally, `env` can be used to get or set individual environment variables.  To display an individual value, use the `env var` syntax.  To set a value, use `env var val` or `env var=val`.  Python value expansion using `$` works as usual.

IPython/core/magics/osm.py

@@ -380,7 +380,16 b' class OSMagics(Magics):'
 
     @line_magic
     def env(self, parameter_s=''):
-        """List environment variables."""
+        """Get, set, or list environment variables.
+
+        Usage:\\
+
+          %env: lists all environment variables/values
+          %env var: get value for var
+          %env var val: set value for var
+          %env var=val: set value for var
+          %env var=$val: set value for var, using python expansion if possible
+        """
         if parameter_s.strip():
             split = '=' if '=' in parameter_s else ' '
             bits = parameter_s.split(split)
@@ -402,7 +411,9 b' class OSMagics(Magics):'
         string.
 
         Usage:\\
-        %set_env var val
+          %set_env var val: set value for var
+          %set_env var=val: set value for var
+          %set_env var=$val: set value for var, using python expansion if possible
         """
         split = '=' if '=' in parameter_s else ' '
         bits = parameter_s.split(split, 1)

docs/source/interactive/shell.rst

@@ -24,6 +24,18 b' the default profile such that:'
  * turn ``%autocall`` to full mode
 
 
+Environment variables
+=====================
+
+Rather than manipulating os.environ directly, you may like to use the magic
+`%env` command.  With no arguments, this displays all environment variables
+and values.  To get the value of a specific variable, use `%env var`.  To set
+the value of a specific variable, use `%env foo bar`, `%env foo=bar`.  By
+default values are considered to be strings so quoting them is unnecessary.
+However, python variables are expanded as usual in the magic command, so
+`%env foo=$bar` means "set the environment variable foo to the value of the
+python variable `bar`".
+
 Aliases
 =======