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Re: one shell command doesn't return result

From: fabien
Subject: Re: one shell command doesn't return result
Date: Sun, 15 Jun 2008 23:56:35 +0200
User-agent: Thunderbird (X11/20080505)

Thank you very much !

Eli Zaretskii a écrit :
Date: Sun, 15 Jun 2008 16:34:16 +0200
From: "address@hidden" <address@hidden>

I would like to make a simple calculation in my makefile, but I have a strange 
On windows, I use the DOS command "set /A 3*100+13/2", it works on a shell and returns 
"306" but not in my makefile. I have make a simple makefile to test it :

# command to make a mathematical operation
CMD_MATH:=$(shell set /A 3*100+13/2)
# command to list files
CMD_FILES:=$(shell dir /b/a-d/-W)

        @echo CMD_MATH:$(CMD_MATH)
        @echo CMD_FILES:$(CMD_FILES)

It returns me :

CMD_FILES:Makefile Makefile~

One command returns correctly the result but not the command "set /A" which 
returns nothing.
I have GNU Make 3.81

This is expected behavior.  "set /?" has this small print among its

    If SET /A is executed from the command line outside of a command
    script, then it displays the final value of the expression.

Note the "outside of a command script" condition: this is the cause of
your surprise.  When Make uses cmd.exe as the shell, it invokes all
the commands through temporary batch files (a.k.a. command scripts);
you can see that if you invoke Make with the --debug=j switch.  And
when "set /a" is invoked from a batch file, it does not print the

The following trick will do what you want:

  CMD_MATH:=$(shell cmd.exe /c "set /A 3*100+13/2")

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