Try to intuit whether typeless file invoked in subprocess

       is an executable image or DCL procedure.

p4raw-id: //depot/vmsperl@5478

2 files changed, 42 insertions, 4 deletions

diff --git a/vms/perlvms.pod b/vms/perlvms.pod
index 53925b2541..3883233c28 100644
--- a/vms/perlvms.pod
+++ b/vms/perlvms.pod
@@ -463,7 +463,11 @@ is executed as a DCL command.  Otherwise, the first token on
 the command line is treated as the filespec of an image to 
 run, and an attempt is made to invoke it (using F<.Exe> and 
 the process defaults to expand the filespec) and pass the 
-rest of C<exec>'s argument to it as parameters.
+rest of C<exec>'s argument to it as parameters.  If the token
+has no file type, and matches a file with null type, then an
+attempt is made to determine whether the file is an executable
+image which should be invoked using C<MCR> or a text file which
+should be passed to DCL as a command procedure.
 
 You can use C<exec> in both ways within the same script, as 
 long as you call C<fork> and C<exec> in pairs.  Perl
@@ -558,9 +562,16 @@ specification (e.g. C<:> or C<]>), an attempt is made to expand it
 using  a default type of F<.Exe> and the process defaults, and if
 successful, the resulting file is invoked via C<MCR>. This allows you
 to invoke an image directly simply by passing the file specification
-to C<system>, a common Unixish idiom.  If LIST consists
-of the empty string, C<system> spawns an interactive DCL subprocess,
-in the same fashion as typiing B<SPAWN> at the DCL prompt.
+to C<system>, a common Unixish idiom.  If the token has no file type,
+and matches a file with null type, then an attempt is made to
+determine whether the file is an executable image which should be
+invoked using C<MCR> or a text file which should be passed to DCL
+as a command procedure.
+
+If LIST consists of the empty string, C<system> spawns an
+interactive DCL subprocess, in the same fashion as typiing
+B<SPAWN> at the DCL prompt.
+
 Perl waits for the subprocess to complete before continuing
 execution in the current process.  As described in L<perlfunc>,
 the return value of C<system> is a fake "status" which follows
diff --git a/vms/vms.c b/vms/vms.c
index 65f1d58995..f1f62bd6eb 100644
--- a/vms/vms.c
+++ b/vms/vms.c
@@ -3393,6 +3393,7 @@ setup_cmddsc(char *cmd, int check_img)
 {
   char vmsspec[NAM$C_MAXRSS+1], resspec[NAM$C_MAXRSS+1];
   $DESCRIPTOR(defdsc,".EXE");
+  $DESCRIPTOR(defdsc2,".");
   $DESCRIPTOR(resdsc,resspec);
   struct dsc$descriptor_s imgdsc = {0, DSC$K_DTYPE_T, DSC$K_CLASS_S, 0};
   unsigned long int cxt = 0, flags = 1, retsts = SS$_NORMAL;
@@ -3448,18 +3449,44 @@ setup_cmddsc(char *cmd, int check_img)
     imgdsc.dsc$a_pointer = s;
     imgdsc.dsc$w_length = wordbreak - s;
     retsts = lib$find_file(&imgdsc,&resdsc,&cxt,&defdsc,0,0,&flags);
+    if (!(retsts&1)) {
+        _ckvmssts(lib$find_file_end(&cxt));
+        retsts = lib$find_file(&imgdsc,&resdsc,&cxt,&defdsc2,0,0,&flags);
     if (!(retsts & 1) && *s == '$') {
+          _ckvmssts(lib$find_file_end(&cxt));
       imgdsc.dsc$a_pointer++; imgdsc.dsc$w_length--;
       retsts = lib$find_file(&imgdsc,&resdsc,&cxt,&defdsc,0,0,&flags);
+          if (!(retsts&1)) {
       _ckvmssts(lib$find_file_end(&cxt));
+            retsts = lib$find_file(&imgdsc,&resdsc,&cxt,&defdsc2,0,0,&flags);
+          }
+    }
     }
+    _ckvmssts(lib$find_file_end(&cxt));
+
     if (retsts & 1) {
+      FILE *fp;
       s = resspec;
       while (*s && !isspace(*s)) s++;
       *s = '\0';
+
+      /* check that it's really not DCL with no file extension */
+      fp = fopen(resspec,"r","ctx=bin,shr=get");
+      if (fp) {
+        char b[4] = {0,0,0,0};
+        read(fileno(fp),b,4);
+        isdcl = isprint(b[0]) && isprint(b[1]) && isprint(b[2]) && isprint(b[3]);
+        fclose(fp);
+      }
+      if (check_img && isdcl) return RMS$_FNF;
+
       if (cando_by_name(S_IXUSR,0,resspec)) {
         New(402,VMScmd.dsc$a_pointer,7 + s - resspec + (rest ? strlen(rest) : 0),char);
+        if (!isdcl) {
         strcpy(VMScmd.dsc$a_pointer,"$ MCR ");
+        } else {
+            strcpy(VMScmd.dsc$a_pointer,"@");
+        }
         strcat(VMScmd.dsc$a_pointer,resspec);
         if (rest) strcat(VMScmd.dsc$a_pointer,rest);
         VMScmd.dsc$w_length = strlen(VMScmd.dsc$a_pointer);