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

[Bruno Haible]

Paul Eggert wrote:
> <https://perlbrew.pl/Dealing-with-shebangs.html> suggests something like the 
> following instead. This would avoid having separate shell scripts and .pl 
> files, 
> which would be a plus:
> 
> #!/bin/sh
> #! −*−perl−*−
> eval 'exec perl −x −wS $0 ${1+"$@"}'
>      if 0;

This does not work for me (with perl 5.22.1), unfortunately:

$ build-aux/useless-if-before-free
Can't open perl script "−x": No such file or directory

Ah, it's because it contains a non-ASCII '−' character! This one works:

#!/bin/sh
#! -*-perl-*-
eval 'exec perl -x -wS $0 ${1+"$@"}'
     if 0;

This one as well:

#!/bin/sh
#! -*-perl-*-
eval 'exec perl -wS -x $0 ${1+"$@"}'
     if 0;

Or this one:

#!/bin/sh
#! -*-perl-*-
eval 'exec perl -wSx $0 ${1+"$@"}'
     if 0;

${1+"$@"} is the same as "$@". Haven't seen a platform that needs
${1+"$@"} in 20 years. See also the discussion in
<https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Shell-Substitutions.html>
 .

And $0 needs to be double-quoted (in case the file name contains a space).

So, I'll use this prologue:

#!/bin/sh
#! -*-perl-*-
eval 'exec perl -wSx "$0" "$@"'
     if 0;


2019-06-15  Bruno Haible  <address@hidden>

        Fix scripts to have valid executable format on Alpine Linux.
        Reported by Tim Rühsen <address@hidden>.
        Idea by Paul Eggert.
        * build-aux/useless-if-before-free: Use a prologue that starts with
        '#!/bin/sh'.
        * build-aux/announce-gen: Likewise.
        * build-aux/gitlog-to-changelog: Likewise.
        * build-aux/prefix-gnulib-mk: Likewise.
        * build-aux/update-copyright: Likewise.
        * tests/test-update-copyright.sh: Update test program accordingly.

diff --git a/build-aux/announce-gen b/build-aux/announce-gen
index 0174f5c..b572833 100755
--- a/build-aux/announce-gen
+++ b/build-aux/announce-gen
@@ -1,6 +1,20 @@
-eval '(exit $?0)' && eval 'exec perl -wS "$0" "$@"'
-  & eval 'exec perl -wS "$0" $argv:q'
-    if 0;
+#!/bin/sh
+#! -*-perl-*-
+# This is a prologue that allows to run a perl script as an executable
+# on systems that are compliant to a POSIX version before POSIX:2017.
+# On such systems, the usual invocation of an executable through execlp()
+# or execvp() fails with ENOEXEC if it is a script that does not start
+# with a #! line.  The script interpreter mentioned in the #! line has
+# to be /bin/sh, because on GuixSD systems that is the only program that
+# has a fixed file name.  The second line is for editing this file in
+# Emacs.  The next two lines below are valid code in both sh and perl.
+# When executed by sh, they re-execute the script through the perl
+# program found in $PATH.  The '-x' option is essential; without it,
+# perl would re-execute the script through /bin/sh.  When executed by
+# perl, the next two lines are a no-op.
+eval 'exec perl -wSx "$0" "$@"'
+     if 0;
+
 # Generate a release announcement message.
 
 my $VERSION = '2018-03-07 03:46'; # UTC
diff --git a/build-aux/gitlog-to-changelog b/build-aux/gitlog-to-changelog
index deddef2..a616b82 100755
--- a/build-aux/gitlog-to-changelog
+++ b/build-aux/gitlog-to-changelog
@@ -1,6 +1,20 @@
-eval '(exit $?0)' && eval 'exec perl -wS "$0" "$@"'
-  & eval 'exec perl -wS "$0" $argv:q'
-    if 0;
+#!/bin/sh
+#! -*-perl-*-
+# This is a prologue that allows to run a perl script as an executable
+# on systems that are compliant to a POSIX version before POSIX:2017.
+# On such systems, the usual invocation of an executable through execlp()
+# or execvp() fails with ENOEXEC if it is a script that does not start
+# with a #! line.  The script interpreter mentioned in the #! line has
+# to be /bin/sh, because on GuixSD systems that is the only program that
+# has a fixed file name.  The second line is for editing this file in
+# Emacs.  The next two lines below are valid code in both sh and perl.
+# When executed by sh, they re-execute the script through the perl
+# program found in $PATH.  The '-x' option is essential; without it,
+# perl would re-execute the script through /bin/sh.  When executed by
+# perl, the next two lines are a no-op.
+eval 'exec perl -wSx "$0" "$@"'
+     if 0;
+
 # Convert git log output to ChangeLog format.
 
 my $VERSION = '2018-03-07 03:47'; # UTC
diff --git a/build-aux/prefix-gnulib-mk b/build-aux/prefix-gnulib-mk
index bef726f..66e138b 100755
--- a/build-aux/prefix-gnulib-mk
+++ b/build-aux/prefix-gnulib-mk
@@ -1,6 +1,19 @@
-eval '(exit $?0)' && eval 'exec perl -wS "$0" "$@"'
-  & eval 'exec perl -wS "$0" $argv:q'
-    if 0;
+#!/bin/sh
+#! -*-perl-*-
+# This is a prologue that allows to run a perl script as an executable
+# on systems that are compliant to a POSIX version before POSIX:2017.
+# On such systems, the usual invocation of an executable through execlp()
+# or execvp() fails with ENOEXEC if it is a script that does not start
+# with a #! line.  The script interpreter mentioned in the #! line has
+# to be /bin/sh, because on GuixSD systems that is the only program that
+# has a fixed file name.  The second line is for editing this file in
+# Emacs.  The next two lines below are valid code in both sh and perl.
+# When executed by sh, they re-execute the script through the perl
+# program found in $PATH.  The '-x' option is essential; without it,
+# perl would re-execute the script through /bin/sh.  When executed by
+# perl, the next two lines are a no-op.
+eval 'exec perl -wSx "$0" "$@"'
+     if 0;
 
 use strict;
 use IO::File;
diff --git a/build-aux/update-copyright b/build-aux/update-copyright
index d80549e..fa9d427 100755
--- a/build-aux/update-copyright
+++ b/build-aux/update-copyright
@@ -1,6 +1,20 @@
-eval '(exit $?0)' && eval 'exec perl -wS -0777 -pi "$0" "$@"'
-  & eval 'exec perl -wS -0777 -pi "$0" $argv:q'
-    if 0;
+#!/bin/sh
+#! -*-perl-*-
+# This is a prologue that allows to run a perl script as an executable
+# on systems that are compliant to a POSIX version before POSIX:2017.
+# On such systems, the usual invocation of an executable through execlp()
+# or execvp() fails with ENOEXEC if it is a script that does not start
+# with a #! line.  The script interpreter mentioned in the #! line has
+# to be /bin/sh, because on GuixSD systems that is the only program that
+# has a fixed file name.  The second line is for editing this file in
+# Emacs.  The next two lines below are valid code in both sh and perl.
+# When executed by sh, they re-execute the script through the perl
+# program found in $PATH.  The '-x' option is essential; without it,
+# perl would re-execute the script through /bin/sh.  When executed by
+# perl, the next two lines are a no-op.
+eval 'exec perl -wSx "$0" "$@"'
+     if 0;
+
 # Update an FSF copyright year list to include the current year.
 
 my $VERSION = '2018-03-07.03:47'; # UTC
diff --git a/build-aux/useless-if-before-free b/build-aux/useless-if-before-free
index 6d6b8d4..0701e7b 100755
--- a/build-aux/useless-if-before-free
+++ b/build-aux/useless-if-before-free
@@ -1,6 +1,20 @@
-eval '(exit $?0)' && eval 'exec perl -wST "$0" "$@"'
-  & eval 'exec perl -wST "$0" $argv:q'
-    if 0;
+#!/bin/sh
+#! -*-perl-*-
+# This is a prologue that allows to run a perl script as an executable
+# on systems that are compliant to a POSIX version before POSIX:2017.
+# On such systems, the usual invocation of an executable through execlp()
+# or execvp() fails with ENOEXEC if it is a script that does not start
+# with a #! line.  The script interpreter mentioned in the #! line has
+# to be /bin/sh, because on GuixSD systems that is the only program that
+# has a fixed file name.  The second line is for editing this file in
+# Emacs.  The next two lines below are valid code in both sh and perl.
+# When executed by sh, they re-execute the script through the perl
+# program found in $PATH.  The '-x' option is essential; without it,
+# perl would re-execute the script through /bin/sh.  When executed by
+# perl, the next two lines are a no-op.
+eval 'exec perl -wSx "$0" "$@"'
+     if 0;
+
 # Detect instances of "if (p) free (p);".
 # Likewise "if (p != 0)", "if (0 != p)", or with NULL; and with braces.
 
diff --git a/tests/test-update-copyright.sh b/tests/test-update-copyright.sh
index f270db5..9ef5344 100755
--- a/tests/test-update-copyright.sh
+++ b/tests/test-update-copyright.sh
@@ -37,9 +37,23 @@ trap 'rm -f $TMP_BASE*' 0 1 2 3 15
 TMP=$TMP_BASE
 s=$TMP-script
 cat <<\EOF > $s
-eval '(exit $?0)' && eval 'exec perl -wS -0777 -pi "$0" "$@"'
-  & eval 'exec perl -wS -0777 -pi "$0" $argv:q'
-    if 0;
+#!/bin/sh
+#! -*-perl-*-
+# This is a prologue that allows to run a perl script as an executable
+# on systems that are compliant to a POSIX version before POSIX:2017.
+# On such systems, the usual invocation of an executable through execlp()
+# or execvp() fails with ENOEXEC if it is a script that does not start
+# with a #! line.  The script interpreter mentioned in the #! line has
+# to be /bin/sh, because on GuixSD systems that is the only program that
+# has a fixed file name.  The second line is for editing this file in
+# Emacs.  The next two lines below are valid code in both sh and perl.
+# When executed by sh, they re-execute the script through the perl
+# program found in $PATH.  The '-x' option is essential; without it,
+# perl would re-execute the script through /bin/sh.  When executed by
+# perl, the next two lines are a no-op.
+eval 'exec perl -wSx "$0" "$@"'
+     if 0;
+
 s/a/b/
 EOF
 chmod a+x $s