Re: Bultin shell variable in Makefile

[Paul Smith]

On Mon, 2009-07-06 at 05:01 -0700, rama krishna wrote:
> 
> Hi All,
> 
> When I am trying to use a predefined shell variable RANDOM in a make
> file.
> I am not able to generate any random value.
> Instead it is showoing as blank.
>  
> The code I am using is : 
>  
> SEED := $(shell /bin/sh -c "$(RANDOM)")
> 
> I am not getting any error but, the value is blank.
> Can anybody help me in solving the problem.

$RANDOM is a special variable in the shell.  But you are using a make
variable $(RANDOM) here, which is not set to anything.  So make expands
this command to "/bin/sh -c """, which does nothing obviously.  So the
result is nothing.

Also, $RANDOM is a special feature of bash; it's not part of a standard
POSIX shell.  So you should be explicitly requesting that the command be
run by bash, not /bin/sh, or it will not be portable.  At least if you
run bash explicitly then systems which don't have bash will see some
kind of error message rather than getting an empty string.

I think you want:

        SEED := $(shell /bin/bash -c "echo $$RANDOM")

(note, not tested!)

-- 
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