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Variable Assignment Consistency

From: Chris Penev
Subject: Variable Assignment Consistency
Date: Thu, 6 Dec 2012 14:12:37 -0800

Dear gnu-make gurus,

I have the following c program (garble.c)

#include <unistd.h>

int main() {

        unsigned char buf[256];
        int           off;

        for(off = 0; off < sizeof buf; off++)
                buf[off] = off;

        return write(1, buf, sizeof buf) != off;

and the following makefile (makefile)

E    ?= $(shell ./garble | tr -d \\000)
$(error $(E))

Running the following commands, give me result which seem inconsistent to me.

$ make 2>&1 | md5sum
6bfaed01fc4f24828ce7014b81c4edf1  -

$ make E="$(./garble | tr -d \\000)" 2>&1 | md5sum
59d743d40047b58aa7829fd38870f288  -

I would expect there to be no difference between the two hashes. My environment is

$ sed q /etc/issue; uname -r; make --version
Debian GNU/Linux wheezy/sid \n \l
GNU Make 3.81
Copyright (C) 2006  Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A

This program built for x86_64-pc-linux-gnu

If instead of piping the output of make to md5sum I convert the output to hex, I see that ...

In one case (the first one)
In the other case (the second one)

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