Command-line variables - in makefile - expand to weird values

Question

From the docs:

Target-specific variables have the same priority as any other makefile variable. Variables provided on the command line (and in the environment if the '-e' option is in force) will take precedence. Specifying the 'override' directive will allow the target-specific variable value to be preferred.

So, a simple makefile, like:

# A pattern-specific variable assignment.
% : foo += file

all : x ;

# Target is a double-colon w/o dependencies, so Make will ALWAYS run its commands.
x ::
    @echo '$(foo)'

Running, we get:

# Override makefile-level variables, with a command-line assignment.
$ make foo=cmd
cmd cmd cmd

# Set the value in the environment, And tell Make to prefer it over any makefile-level definitions.
$ foo=env make --environment-overrides
env file file

Returning now, to the quote above, from the documentation:

Variables provided on the command line (and in the environment if the '-e' option is in force) will take precedence.

It seems, that using either:

Command-line assignment.
Environment-set variables, AND using -e (--environment-overrides).

Have both the same effect, i.e. overrides the file-level (makefile) variable.

But, the results differ greatly. Remember that the value given in the command-line was: cmd, and the value given in the environment was: env.

Now, compare the values, given for a command-line override vs. an environment override:

cmd cmd cmd (for command-line override).
env file file (for environment override).

So, whereas for command-line, Make repeats the same value, i.e. cmd, 3 times, for environment-override, the situation is different. That is, Make will "repeat" the environment-level value: env only 1 time, and then repeats - none other - than the overridden file-level value: file.

Now, not only is the situation completely different for an "override" from command-line vs. an "override" from the environment, which is strange by itself, the problem here is much bigger.

Since, Make rules to give "priority" for a command-line (or environment) value, why does it insist to append "other" values (as in the case of environment-override, where Make appends "file file"), or in the case of a command-line override (where Make repeats the same value ***3* times). Seriously?

How does it make sense at all? And what is the justification for these inconsistent and strange results?

The env file file result makes sense to me; the cmd cmd cmd result makes no sense. I am having to guess at why there are two additions (rather than just one) to the basic foo macro, too. I'll observe that if you happen to have a file x in your directory, the echo command won't be executed. — Jonathan Leffler
The reason there's two additions is that there's one from the all target and one from the x target, as both match %. — Toby Speight
You are that person who posted all those oddly formatted bullet lists of complaints about make a while back aren't you? If you have bugs you wish to report to the make developers then do that. This isn't an appropriate forum for that. If you are actually interested in diagnosis of potentially-correct-but-odd behavior then I would suggest relaxing your tone a bit. — Etan Reisner
cmd cmd cmd is the easy case. env file file is the odd one. Answering. — Etan Reisner

Etan Reisner Etan Reisner · Accepted Answer · 2015-08-20T04:26:27

I believe the answer here is related to the answer to this other question of yours. (And possibly a bug in the env override version.)

The global variables and the target-specific variables are distinct variables.

The cmd cmd cmd result is because when you write %: foo += file make stores that as an addition to the current value of variable foo of the target-specific value of the variable foo which is file.

However, when you set foo on the command line make overrides the value of the target-specific variable foo to be cmd instead of file. So when make concats the variable each time it gets cmd cmd cmd.

That explanation should, I think, get you env env env then and I'm not sure why it doesn't. This could be a bug or it could be some other detail about how env override variables and target-specific variable values work. I'm not sure.

(Check the output of make -p for both these cases to see what I mean about the target-specific variable's value.)

Command-line variables - in makefile - expand to weird values

1 Answers