Merge topic 'env'

860338491e Help: Describe $CACHE and $ENV as operators
e855bd5248 Help: Document if(DEFINED ENV{name})
8ba2a8d4a4 Help: short/long variable reference in if command
85498fccd8 Help: Provide backreferences.
e24ef96942 Help: New section on Environment Variables in cmake-language.7
e4554149c4 Help: Remove over-precise clause.
3de551cc22 Help: Clarify effect of set(ENV{..} ..) and unset(ENV{..})

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !2538

3 files changed, 31 insertions, 10 deletions

diff --git a/Help/command/if.rst b/Help/command/if.rst
index 4781f35..1cd9965 100644
--- a/Help/command/if.rst
+++ b/Help/command/if.rst
@@ -187,10 +187,11 @@ Possible conditions are:
 ``if(<variable|string> IN_LIST <variable>)``
  True if the given element is contained in the named list variable.
 
-``if(DEFINED <variable>)``
- True if the given variable is defined.  It does not matter if the
- variable is true or false just if it has been set.  (Note macro
- arguments are not variables.)
+``if(DEFINED <name>|ENV{<name>})``
+ True if a variable or environment variable
+ with given ``<name>`` is defined.
+ The value of the variable does not matter.
+ Note that macro arguments are not variables.
 
 ``if((condition) AND (condition OR (condition)))``
  The conditions inside the parenthesis are evaluated first and then
@@ -231,7 +232,7 @@ which is true because ``var2`` is defined to "var1" which is not a false
 constant.
 
 Automatic evaluation applies in the other cases whenever the
-above-documented signature accepts ``<variable|string>``:
+above-documented condition syntax accepts ``<variable|string>``:
 
 * The left hand argument to ``MATCHES`` is first checked to see if it is
   a defined variable, if so the variable's value is used, otherwise the
@@ -269,3 +270,8 @@ specified in a :ref:`Quoted Argument` or a :ref:`Bracket Argument`.
 A quoted or bracketed variable or keyword will be interpreted as a
 string and not dereferenced or interpreted.
 See policy :policy:`CMP0054`.
+
+There is no automatic evaluation for environment or cache
+:ref:`Variable References`.  Their values must be referenced as
+``$ENV{<name>}`` or ``$CACHE{<name>}`` wherever the above-documented
+condition syntax accepts ``<variable|string>``.
diff --git a/Help/command/set.rst b/Help/command/set.rst
index e37e693..dd5ea13 100644
--- a/Help/command/set.rst
+++ b/Help/command/set.rst
@@ -88,4 +88,10 @@ Set Environment Variable
 
   set(ENV{<variable>} <value>...)
 
-Sets the current process environment ``<variable>`` to the given value.
+Sets an :manual:`Environment Variable <cmake-env-variables(7)>`
+to the given value.
+Subsequent calls of ``$ENV{<variable>}`` will return this new value.
+
+This command affects only the current CMake process, not the process
+from which CMake was called, nor the system environment at large,
+nor the environment of subsequent build or test processes.
diff --git a/Help/command/unset.rst b/Help/command/unset.rst
index 1a5e49f..7521052 100644
--- a/Help/command/unset.rst
+++ b/Help/command/unset.rst
@@ -3,6 +3,9 @@ unset
 
 Unset a variable, cache variable, or environment variable.
 
+Unset Normal Variable or Cache Entry
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 .. code-block:: cmake
 
   unset(<variable> [CACHE | PARENT_SCOPE])
@@ -22,11 +25,17 @@ If ``PARENT_SCOPE`` is present then the variable is removed from the scope
 above the current scope.  See the same option in the :command:`set` command
 for further details.
 
-``<variable>`` can be an environment variable such as:
+Unset Environment Variable
+^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. code-block:: cmake
 
-  unset(ENV{LD_LIBRARY_PATH})
+  unset(ENV{<variable>})
+
+Removes ``<variable>`` from the currently available
+:manual:`Environment Variables <cmake-env-variables(7)>`.
+Subsequent calls of ``$ENV{<variable>}`` will return the empty string.
 
-in which case the variable will be removed from the current
-environment.
+This command affects only the current CMake process, not the process
+from which CMake was called, nor the system environment at large,
+nor the environment of subsequent build or test processes.