perl_{exe,version}: more robust

Author: scivision

+stdlib/normalize.m

@@ -13,7 +13,7 @@
 function [n, b] = normalize(file, backend)
 arguments
   file string
-  backend (1,:) string = ["java", "python", "native"]
+  backend (1,:) string = ["native", "java", "python"]
 end
 
 o = stdlib.Backend(mfilename(), backend);

+stdlib/perl_exe.m

@@ -17,6 +17,8 @@
 if s == 0 && isfile(r)
   exe = r;
   perle = r;
+else
+  exe = string.empty;
 end
 
 end

+stdlib/perl_version.m

@@ -15,14 +15,18 @@
   return
 end
 
-cmd = sprintf('"%s" -e "print $^V"', stdlib.perl_exe());
+v = [];
 
-[s, r] = system(cmd);
+exe = stdlib.perl_exe();
 
-if s == 0
-  v = sscanf(r, 'v%d.%d.%d').';
-else
-  v = [];
+if ~stdlib.strempty(exe)
+  cmd = sprintf('"%s" -e "print $^V"', exe);
+
+  [s, r] = system(cmd);
+
+  if s == 0
+    v = sscanf(r, 'v%d.%d.%d').';
+  end
 end
 
 % cache the result - even if empty -- because the check takes up to 1000 ms say on HPC

+stdlib/private/executable.pl

@@ -3,9 +3,24 @@
 # we do not use $Config{perlpath} as that's a build-time variable and is thus
 # incorrect when a buildbot was used e.g. Windows Perl from Matlab
 #
-# https://perldoc.perl.org/Cwd#abs_path
-# abs_path is effectively realpath(3)
+# Cwd::abs_path is not appropriate as it does not actually work like realpath(3)
+#
+# does not interact with filesystem:
+# https://perldoc.perl.org/File::Spec#file_name_is_absolute
+#
+# works like which() but platform-independent
+# https://perldoc.perl.org/IPC::Cmd#$path-=-can_run(-PROGRAM-);
+
+use File::Spec;
+use IPC::Cmd 'can_run';
+
+my $perl_exe = $^X;
+my $perl_path;
 
-use Cwd 'abs_path';
+if (File::Spec->file_name_is_absolute($perl_exe)) {
+  $perl_path = $perl_exe;
+} else {
+  $perl_path = can_run($perl_exe);
+}
 
-print abs_path($^X);
+print $perl_path;