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Re: Variable Assignment Consistency

From: Paul Smith
Subject: Re: Variable Assignment Consistency
Date: Thu, 06 Dec 2012 18:14:08 -0500

On Thu, 2012-12-06 at 14:12 -0800, Chris Penev wrote:
> I would expect there to be no difference between the two hashes.

That expectation would not be correct, clearly :-).  Make has its own
escaping and expanding procedures that it follows, in addition to /
aside from what the shell does.

> 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) 
>       * make converts the newline character to a space.
> In the other case (the second one) 
>       * make does not convert the newline character to a space 
>       * make deletes the characters \044 \045 
>                       * leading me to think make tried to expand $% as
>                         a variable. 

You have perfectly captured the differences.  They are easily

>From the GNU make manual description of the $(shell ...) function:

           The `shell' function performs the same function that backquotes
        (``') perform in most shells: it does "command expansion".  This means
        that it takes as an argument a shell command and evaluates to the
        output of the command.  The only processing `make' does on the result
        is to convert each newline (or carriage-return / newline pair) to a
        single space.  If there is a trailing (carriage-return and) newline it
        will simply be removed.

In the second case, you are assigning a value to a variable (that is,
make sees just an assignment like "E=abcedfg$%hijk" or whatever, and
values are always expanded.

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