[lmi-commits] [lmi] master 07a02d3 1/4: Purify sourcing demonstration by removing a desirable refinement

[Greg Chicares]

branch: master
commit 07a02d3cc805e0d736bae90124387cc64e4fc145
Author: Gregory W. Chicares <address@hidden>
Commit: Gregory W. Chicares <address@hidden>

    Purify sourcing demonstration by removing a desirable refinement
    
    Moved commands to set 'make' variables out of the shell script and back
    into the makefile.
    
    The parent commit is preferable for actual use. See:
      https://lists.nongnu.org/archive/html/lmi/2019-05/msg00052.html
    et seq.
    
    Ask the internet how to source a shell script in a makefile, and it will
    answer that it simply can't be done--that the script must be changed.
    This revision proves that it can be done, without changing the script.
    That is this demonstration's purpose: to show how it can be done,
    regardless of whether it should be done in exactly this way.
---
 gwc/parent.make | 21 +++++++++++++++------
 gwc/set.sh      | 10 +---------
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/gwc/parent.make b/gwc/parent.make
index 81fd3eb..e835b9a 100644
--- a/gwc/parent.make
+++ b/gwc/parent.make
@@ -5,10 +5,9 @@
 #  - give the top-level makefile a target to remake itself, with
 #     - $(eval include $(LMI_ENV_FILE)) in its recipe, and
 #     - $(LMI_ENV_FILE) as a prerequisite
-#  - add a phony $(LMI_ENV_FILE) target that sources the script
-#  - make the script write 'make' assignments like "export foo := bar"
-#    for each desired environment variable to a file named
-#    $LMI_ENV_FILE, iff that filename is of nonzero length
+#  - add a phony $(LMI_ENV_FILE) target whose recipe sources the
+#    script and writes 'make' assignments like "export foo := bar"
+#    into the file it names
 # To test:
 #   $export LMI_IN=Russia;   make -f parent.make all
 #   $export LMI_IN=Mongolia; make -f parent.make all
@@ -22,14 +21,24 @@ parent.make:: $(LMI_ENV_FILE)
        rm $(LMI_ENV_FILE)
 
 $(LMI_ENV_FILE):
-       @echo "Sourcing 'set.sh'"; \
-       . ./set.sh ; \
+       @echo "Sourcing 'set.sh'"
+       @. ./set.sh ; \
+         { \
+           echo "export LMI_OUT1 := $$LMI_OUT1"; \
+           echo "export LMI_OUT2 := $$LMI_OUT2"; \
+         } > $@ ; \
        echo "'$$LMI_IN' --> '$$LMI_OUT1', '$$LMI_OUT2' : sourced in 
'parent.make'"
 
 all:
        @echo "'$$LMI_IN' --> '$$LMI_OUT1', '$$LMI_OUT2' : targets in 
'parent.make'"
        $(MAKE) --no-print-directory -f child.make
 
+# For real-world use, commit 3ff6c008 seems preferable. It writes
+# 'make' assignments in the script rather than in this makefile,
+# facilitating maintenance by keeping the list of variables in a
+# single file. See this discussion:
+#   https://lists.nongnu.org/archive/html/lmi/2019-05/msg00052.html
+
 # Obviously one could simply write a cover script to replace direct
 # invocation of 'make', but that's nasty. See:
 #   https://lists.gnu.org/archive/html/help-make/2006-04/msg00142.html
diff --git a/gwc/set.sh b/gwc/set.sh
index 0660dc9..924fc58 100755
--- a/gwc/set.sh
+++ b/gwc/set.sh
@@ -2,10 +2,8 @@
 
 foo()
 {
-# $LMI_ENV_FILE is defined by the makefile that sources this script.
-# shellcheck disable=SC2154
-echo "LMI_ENV_FILE in 'set.sh': $LMI_ENV_FILE"
 echo "'$LMI_IN' --> '$LMI_OUT1', '$LMI_OUT2' : entering 'set.sh'"
+
 export LMI_OUT1="$LMI_IN"
 export LMI_OUT2="$LANG"
 
@@ -16,12 +14,6 @@ case "$LMI_IN" in
 esac
 
 echo "'$LMI_IN' --> '$LMI_OUT1', '$LMI_OUT2' : leaving 'set.sh'"
-if [ -n "$LMI_ENV_FILE" ]; then
-    {
-    echo "export LMI_OUT1 := $LMI_OUT1"
-    echo "export LMI_OUT2 := $LMI_OUT2"
-    } > "$LMI_ENV_FILE"
-fi
 }
 
 foo