URL:
<https://savannah.gnu.org/bugs/?63621>
Summary: Enhancement request - new built in variables
Project: make
Submitter: None
Submitted: Wed 04 Jan 2023 03:56:14 PM UTC
Severity: 3 - Normal
Item Group: Enhancement
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Component Version: None
Operating System: None
Fixed Release: None
Triage Status: None
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Follow-up Comments:
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Date: Wed 04 Jan 2023 03:56:14 PM UTC By: Anonymous
See discussion in
https://stackoverflow.com/questions/74707248/using-call-in-a-makefile-recipe
There are multiple use cases where it would be nice for a shell operation or
the expansion of a string to be able to detect if it's within a makefile
recipe or makefile body.
Specific use case:
I wanted to execute a shell command that returned a string that is later used
(either echoed immediately or passed on to another program)
I used a $(call...) to pass parameters from the parent Makefile, but found it
did not work in recipes as it is executed at read-in time rather than shell
invocation time.
e.g. within the body it would be $(shell echo $(call fn,$(var))), which worked
fine. But in the recipe it would be echo "some text" where "some text" is the
premature expansion of echo $(call fn,$(var)). BTW $(info...) can't be used
in the first example as the return is not always 7 bit ASCII. $(info) seems
to fail with UTF.
Suggested use cases:
- Allow a different shell in $(shell...) and recipe without explicitly
invoking it each time.
- Allow a $(call...) to act differently in a recipe and when invoked in a
$(shell), $(info) etc.
- Allow the build environemtn host and the build job host to be different
operating system or OS versions.
Tried so far?
I've done some tests and I can't find a set of enviroment conditions that can
easily be used to detect if expanded within a recipe or not. (See
https://gist.github.com/the-moog/62679586e9fba7448c8b07824565bb66)
I can work round this by pre-calculating the resulting text before the recipe
is called, then only returning the one that is meaningful, but that is all a
bit hacky.
I think there is a simple enhancement that would cover all of the above....
(Note: Examples for illustration only)
My Suggestions:
1: Add a .RECIPE_SHELL variable that defaults to .SHELL unless override is
used.
simple example:
.SHELL = /bin/bash
override .RECIPE_SHELL := /bin/tcsh
# Execute a bash statement
res = $(shell $$((2+2)))
# Execute a tcsh statement
all:
<TAB>setenv res $(RES); echo "res=$${res}"
----
2: Add a .IN_RECIPE variable that evaluates to '1' if expanded within a recipe
and '' otherwise.
simple example:
myprog := echo
target := all
deps :=
# The hello macro
define hello =
$(if $(.IN_RECIPE),$(myprog) "$1",$(shell $(myprog) "$1" >> /dev/stderr))
endef
# Say hello
$(call hello, world from make)
# Do something with a previously unknown result
$(target): $(deps) | $(call hello, Installing recipe for $(target))
<TAB>$(call hello, world from recipe)
<TAB>if something; then \
<TAB> $(call hello, it did something);\
<TAB>else \
<TAB> $(call hello, something went wrong);\
<TAB>fi
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