Re: Alpine: useless-if-before-free: Exec format error

[Bruno Haible]

Paul Eggert wrote:
> Perhaps we 
> should just prepend "#!/bin/sh" or "#!/usr/bin/env perl" (not sure 
> which) and let people on weird systems fix things by hand.

"#!/usr/bin/env perl" does not work on GuixSD (where the only program
that has a hardcoded file name is /bin/sh; there is no /usr and no
/bin/env on this distro).

Naively prepending "#!/bin/sh" leads to this (with perl 5.22.1):

$ build-aux/useless-if-before-free
/bin/sh: 0: Illegal option -w

$ strace -f build-aux/useless-if-before-free 2>&1 | grep ^exec
execve("build-aux/useless-if-before-free", 
["build-aux/useless-if-before-free"], [/* 79 vars */]) = 0
execve("/home/bruno/bin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/home/bruno/local/bin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/darch/x86_64-linux-gnu/gnu/bin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/arch/local/x86_64-linux-gnu/bin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/arch/local/x86_64-linux/bin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/usr/local/sbin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/usr/local/bin/perl", ["perl", "-wST", 
"build-aux/useless-if-before-free"], [/* 79 vars */]) = -1 ENOENT (No such file 
or directory)
execve("/usr/sbin/perl", ["perl", "-wST", "build-aux/useless-if-before-free"], 
[/* 79 vars */]) = -1 ENOENT (No such file or directory)
execve("/usr/bin/perl", ["perl", "-wST", "build-aux/useless-if-before-free"], 
[/* 79 vars */]) = 0
execve("/bin/sh", ["/bin/sh", "-wST", "build-aux/useless-if-before-free"], [/* 
79 vars */]) = 0

So, what you can see is that the redirect from /bin/sh to perl works right.
But perl then sees the first line and redirects back to /bin/sh. In other
words, there is logic in perl that amounts to "I refuse to be executed
through scripts that start with '#!/bin/sh'".

This finding is confirmed by the following comment in the perl source code:
/* ALTERNATE_SHEBANG:
 *      This symbol, if defined, contains a "magic" string which may be used
 *      as the first line of a Perl program designed to be executed directly
 *      by name, instead of the standard Unix #!.  If ALTERNATE_SHEBANG
 *      begins with a character other then #, then Perl will only treat
 *      it as a command line if it finds the string "perl" in the first
 *      word; otherwise it's treated as the first line of code in the script.
 *      (IOW, Perl won't hand off to another interpreter via an alternate
 *      shebang sequence that might be legal Perl code.)
 */

I propose this solution:

  - Rename 'useless-if-before-free' to 'useless-if-before-free.pl',
    removing the first 3 lines, and removing the execute permission.
    Also update the reference to ME in the --help output.

  - Add a shell script useless-if-before-free that merely does this:

     #!/bin/sh
     exec perl "$0".pl "$@"

  - Update the module description, to list both
    build-aux/useless-if-before-free and build-aux/useless-if-before-free.pl.

And likewise for the other programs:

  build-aux/gitlog-to-changelog
  build-aux/update-copyright
  build-aux/announce-gen
  build-aux/prefix-gnulib-mk
  tests/test-update-copyright.sh

Bruno