Eliminate direct use of os.getenv in sage.interfaces

[mkoeppe]

... as shown by git grep getenv, environment variables such as SAGE_MACAULAY2_COMMAND are checked.

These should go through variables defined in sage.env (and perhaps through sage.feature, Executable.absolute_filename(), #31296) so that they can be configured using sage_conf as well.

(see also #32867 comment:31 to #32867 comment:36)

See also: #32957 Replace have_program usage by Features

• Depends on sage.features.Executable: Prepend $SAGE_VENV/bin:$SAGE_LOCAL/bin to PATH #31296
• Depends on FriCAS spkg-configure and Feature #35838

CC: @kiwifb @antonio-rojas @fchapoton @orlitzky @tornaria @dimpase

Component: refactoring

Issue created by migration from https://trac.sagemath.org/ticket/33405

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,5 +1,5 @@
 ... as shown by `git grep getenv`.
 
-These should go through variables defined in `sage.env` (and perhaps through `sage.feature`) so that they can be configured using `sage_conf` as well.
+These should go through variables defined in `sage.env` (and perhaps through `sage.feature`, `Executable.absolute_filename()`, #31296) so that they can be configured using `sage_conf` as well.
 
 

[mkoeppe]

Dependencies: #31296

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,4 +1,4 @@
-... as shown by `git grep getenv`.
+... as shown by `git grep getenv`, environment variables such as `SAGE_MACAULAY2_COMMAND` are checked.
 
 These should go through variables defined in `sage.env` (and perhaps through `sage.feature`, `Executable.absolute_filename()`, #31296) so that they can be configured using `sage_conf` as well.
 

[mkoeppe]

Description changed:

--- 
+++ 
@@ -2,4 +2,4 @@
 
 These should go through variables defined in `sage.env` (and perhaps through `sage.feature`, `Executable.absolute_filename()`, #31296) so that they can be configured using `sage_conf` as well.
 
-
+(see also [#32867 comment:31](https://github.com/sagemath/sage/issues/32867#comment:31) to [#32867 comment:36](https://github.com/sagemath/sage/issues/32867#comment:36))

[mkoeppe]

Description changed:

--- 
+++ 
@@ -3,3 +3,6 @@
 These should go through variables defined in `sage.env` (and perhaps through `sage.feature`, `Executable.absolute_filename()`, #31296) so that they can be configured using `sage_conf` as well.
 
 (see also [#32867 comment:31](https://github.com/sagemath/sage/issues/32867#comment:31) to [#32867 comment:36](https://github.com/sagemath/sage/issues/32867#comment:36))
+
+See also: #32957 Replace `have_program` usage by Features
+