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Re: [Tinycc-devel] env executable examples

From: grischka
Subject: Re: [Tinycc-devel] env executable examples
Date: Fri, 11 May 2012 14:08:47 +0200
User-agent: Thunderbird (Windows/20100228)

Michael Matz wrote:

On Thu, 10 May 2012, grischka wrote:

[1] See commit 27a428cd0fae475d7377e1dbe218c064ee217d85

Basically /usr/bin/env tcc -run will try to find "tcc -run" which is then obviously not found. Should we go back to the solution proposed in [2] or do you have another idea?

Why not use just

    #!tcc -tun

Because shebangs are interpreted by the kernel VFS, which doesn't know about $PATH, and hence won't find 'tcc' in any path (and therefore the execution will fail). That's what env(1) was intended for, but the linux kernel unfortunately supports only exactly one (optional) argument for the interpreter, i.e. it breaks with two and more arguments like when the shebang is "#!env firstarg secondarg". So, all in all, when you use an meta-interpreter (like env) that somehow needs the name of the real interpreter as argument (tcc in this case) you can't give further arguments to that real interpreter (-run here).

Ok, thanks.  I'm finally able to understand now the deal with the
'expand_args' stuff here:

            case TCC_OPTION_run:
                int argc1;
                char **argv1;
                argc1 = expand_args(&argv1, optarg);
                if (argc1 > 0) {
                    parse_args(s, argc1, argv1);
                multiple_files = 0;
                output_type = TCC_OUTPUT_MEMORY;

Otherwise I'd suggest to revert to the original

    #!/usr/local/bin/tcc -tun

Which again would have the problem of hardcoding the path to tcc into the "scripts". You need a meta-interpreter for finding the name of the real interpreter, and you can't give further arguments to it. Hence the best suggestion up to now was to create a wrapper script called tcc-run (just calling "exec tcc -run $1" on its argument), which would be used as argument to the 'env' shebang.

Of course, one could also decide to not care, but IMHO Davids above suggestion (helper script) is the most satisfying one, given the sorry circumstances.

Indeed it's sorry because my admittedly rather limited understanding
of shebang scripts is usage as simple as in


Now the examples ex1.c and ex4.c are meant to show off how tcc can be
used as an interpreter for C-scripts in a rather similar way, in
particular also with additional arguments such as in ex4.c:

    #!/usr/local/bin/tcc -run -L/usr/X11R6/lib -lX11

Obviously the original intention (seen the 'expand_args' hack above)
is to make that possible without any additional wrapper script.  The
point of the examples is to show that intention.  If we provide a
wrapper script we would miss that point in the first place.

Also, if I'd install perl elsewhere, quite some things will stop to
work just as well.  IMO it is not the point of our examples to show
how to escape from this system limitation.

My 2 cents.

--- grischka


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