Re: Handling of shell builtins in make(1)

From: Scott Long (scottl_at_samsco.org)
Date: 05/24/05

  • Next message: Harti Brandt: "Re: Handling of shell builtins in make(1)" 
    Date: Mon, 23 May 2005 20:50:40 -0600
To: Harti Brandt <harti@freebsd.org>

    Harti Brandt wrote:

    >
    > Hi all,
    >
    > I think I found a problem in the shell code in make(1), but I'm not sure
    > whether to fix it or not and how. The problem is as follows: in compat
    > mode (this is the default mode when make(1) is not called with -j) the
    > command lines of a target are executed by one shell per line (this is
    > also how Posix wants it). To reduce the number of shells make does an
    > optimisation: when the command line does not contain one of a
    > pre-defined set of meta characters and does not start with one of a
    > predefined set of shell builtins, make directly exec's the command
    > instead of using an intermediate shell. The problem is that the current
    > list of builtins is limited to:
    >
    > alias cd eval exec exit read set ulimit unalias umask unset wait
    >
    > Obviously this is not the full set of shell builtins and does also not
    > contain the shell reserved words.
    >
    > The result of this is that for one and the same command you can get
    > different behaviour whether you execute it via make(1) or via sh -c '...'.
    > As an example take echo(1). When called via the sh -c you get the builtin
    > echo which supports the -e option, when executed by make(1) you get
    > /bin/echo which doesn't. If you suddenly include a shell meta character
    > in the command line:
    >
    > foo:
    > echo "MAKEFLAGS: ${MAKEFLAGS}"
    >
    > you suddenly get also the builtin (':' is a meta character).
    >
    > For the reserved words the situation is almost the same. With the
    > following makefile:
    >
    > foo:
    > if
    >
    > one gets:
    >
    > if:No such file or directory, while
    >
    > foo:
    > if [ -x /bin/sh ] ; then echo hey ; fi
    >
    > you get what you expect.
    >
    > I think all this may be very confusing. The question is what to do. I
    > see the following options:
    >
    > 1. leave it as it is.
    >
    > 2. include the Posix reserved words and builtins into the list.
    >
    > 3. include all reserved words and builtins of our shell into the list.
    >
    > Option (3) is probably best. With (2) you still get different behaviour
    > for the two command lines in:
    >
    > foo:
    > bind -h
    > bind -h *
    >
    > (the first line will try to find bind in the path while the second will
    > execute the shell builtin).
    >
    > Opinions?
    >
    > harti

    4. Separate /bin/sh into a front end and back end (libsh) and include
    libsh into make.

    (running and hiding as I hit the 'send' key)

    Scott
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  • Next message: Harti Brandt: "Re: Handling of shell builtins in make(1)"

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