Date: Mon, 23 May 2005 15:51:16 +0200 (CEST) From: Harti Brandt <hartmut.brandt@dlr.de> To: arch@freebsd.org Subject: Handling of shell builtins in make(1) Message-ID: <20050523153118.C28521@beagle.kn.op.dlr.de>
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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
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