docs: add short documentation for export

Work on #10541.

doc_src/cmds/export.rst

@@ -0,0 +1,43 @@
+.. _cmd-export:
+
+export - compatibility function for exporting variables
+=======================================================
+
+Synopsis
+--------
+
+.. synopsis::
+
+    export
+    export NAME=VALUE
+
+
+Description
+-----------
+
+``export`` is a function included for compatibility with POSIX shells. In general, the :doc:`set <set>` 
+builtin should be used instead.
+
+When called without arguments, ``export`` prints a list of currently-exported variables, like ``set
+-x``.
+
+When called with a ``NAME=VALUE`` pair, the variable ``NAME`` is set to ``VALUE`` in the global
+scope, and exported as an environment variable to other commands.
+
+There are no options available.
+
+Example
+-------
+
+The following commands have an identical effect.
+
+::
+
+    set -gx PAGER bat
+    export PAGER=bat
+
+
+See more
+--------
+
+1. The :doc:`set <set>` command.

doc_src/commands.rst

@@ -79,6 +79,7 @@ Some helper functions, often to give you information for use in your prompt:
 - :doc:`fish_add_path <cmds/fish_add_path>` to easily add a path to $PATH.
 - :doc:`alias <cmds/alias>` to quickly define wrapper functions ("aliases").
 - :doc:`fish_delta <cmds/fish_delta>` to show what you have changed from the default configuration.
+- :doc:`export <cmds/export>` as a compatibility function for other shells.
 
 Helper commands
 ^^^^^^^^^^^^^^^