Fix scripts to have valid executable format on Alpine Linux.

Reported by Tim Rühsen <tim.ruehsen@gmx.de>.
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.

1 files changed, 17 insertions, 3 deletions

diff --git a/build-aux/gitlog-to-changelog b/build-aux/gitlog-to-changelog
index deddef2446..a616b82343 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