Process options first.

Change command line processing to go through all of the options
and associated parameters first, and then go through the command
line again, processing the file names using the resolved options.
In addition, if "-" follows a "--", then consider the "-" to be
a file name instead of stdin. Both of these changes are to be more
compatible with gzip, and are not compatible with the previous
versions of pigz, which would process the options and file names
in the sequence they appear.

pigz.1

@@ -95,6 +95,10 @@ or
 .B -tp 1
 ).
 .PP
+All options on the command line are processed before any names are processed.
+If no names are provided on the command line, or if "-" is given as a name (but
+not after "--"), then the input is taken from stdin.
+.PP
 Compressed files can be restored to their original form using
 .I pigz -d
 or

pigz.c

@@ -4087,7 +4087,7 @@ local size_t num(char *arg) {
     return val;
 }
 
-// Process an option, return true if a file name and not an option.
+// Process an argument, return true if it is an option (not a filename)
 local int option(char *arg) {
     static int get = 0;     // if not zero, look for option parameter
     char bad[3] = "-X";     // for error messages (X is replaced)
@@ -4098,13 +4098,13 @@ local int option(char *arg) {
         throw(EINVAL, "missing parameter after %s", bad);
     }
     if (arg == NULL)
-        return 0;
+        return 1;
 
     // process long option or short options
     if (*arg == '-') {
         // a single dash will be interpreted as stdin
         if (*++arg == 0)
-            return 1;
+            return 0;
 
         // process long option (fall through with equivalent short option)
         if (*arg == '-') {
@@ -4144,7 +4144,6 @@ local int option(char *arg) {
                 }
                 if (g.level == 10 || g.level > 11)
                     throw(EINVAL, "only levels 0..9 and 11 are allowed");
-                new_opts();
                 break;
 #ifndef NOZOPFLI
             case 'F':  g.zopts.blocksplittinglast = 1;  break;
@@ -4200,7 +4199,7 @@ local int option(char *arg) {
             }
         } while (*++arg);
         if (*arg == 0)
-            return 0;
+            return 1;
     }
 
     // process option parameter for -b, -p, -S, -I, or -J
@@ -4217,7 +4216,6 @@ local int option(char *arg) {
                 (ssize_t)OUTPOOL(g.block) < 0 ||
                 g.block > (1UL << 29))          // limited by append_len()
                 throw(EINVAL, "block size too large: %s", arg);
-            new_opts();
         }
         else if (get == 2) {
             n = num(arg);
@@ -4230,7 +4228,6 @@ local int option(char *arg) {
             if (g.procs > 1)
                 throw(EINVAL, "compiled without threads");
 #endif
-            new_opts();
         }
         else if (get == 3)
             g.sufx = arg;                       // gz suffix
@@ -4241,11 +4238,11 @@ local int option(char *arg) {
             g.zopts.blocksplittingmax = (int)num(arg);  // max block splits
 #endif
         get = 0;
-        return 0;
+        return 1;
     }
 
     // neither an option nor parameter
-    return 1;
+    return 0;
 }
 
 #ifndef NOTHREAD
@@ -4258,8 +4255,8 @@ local void cut_yarn(int err) {
 // Process command line arguments.
 int main(int argc, char **argv) {
     int n;                          // general index
-    int noop;                       // true to suppress option decoding
-    unsigned long done;             // number of named files processed
+    int nop;                        // index before which "-" means stdin
+    int done;                       // number of named files processed
     size_t k;                       // program name length
     char *opts, *p;                 // environment default options, marker
     ball_t err;                     // error information from throw()
@@ -4309,12 +4306,12 @@ int main(int argc, char **argv) {
                     p++;
                 n = *p;
                 *p = 0;
-                if (option(opts))
+                if (!option(opts))
                     throw(EINVAL, "cannot provide files in "
                                   "GZIP environment variable");
                 opts = p + (n ? 1 : 0);
             }
-            option(NULL);
+            option(NULL);           // check for missing parameter
         }
 
         // process user environment variable defaults in PIGZ as well
@@ -4328,12 +4325,12 @@ int main(int argc, char **argv) {
                     p++;
                 n = *p;
                 *p = 0;
-                if (option(opts))
+                if (!option(opts))
                     throw(EINVAL, "cannot provide files in "
                                   "PIGZ environment variable");
                 opts = p + (n ? 1 : 0);
             }
-            option(NULL);
+            option(NULL);           // check for missing parameter
         }
 
         // decompress if named "unpigz" or "gunzip", to stdout if "*cat"
@@ -4353,25 +4350,29 @@ int main(int argc, char **argv) {
         if (argc < 2 && isatty(g.decode ? 0 : 1))
             help();
 
-        // process command-line arguments
-        done = noop = 0;
+        // process all command-line options first
+        nop = argc;
         for (n = 1; n < argc; n++)
-            // ignore options after "--"
-            if (noop == 0 && strcmp(argv[n], "--") == 0) {
-                noop = 1;
-                option(NULL);
+            if (strcmp(argv[n], "--") == 0) {
+                nop = n;                // after this, "-" is the name "-"
+                argv[n] = NULL;         // remove option
+                break;                  // ignore options after "--"
             }
-            // process argument, interpreting if option
-            else if (noop || option(argv[n])) {
-                // argv[n] is a name to process
+            else if (option(argv[n]))   // process argument
+                argv[n] = NULL;         // remove if option
+        option(NULL);                   // check for missing parameter
+
+        // process command-line filenames
+        done = 0;
+        for (n = 1; n < argc; n++)
+            if (argv[n] != NULL) {
                 if (done == 1 && g.pipeout && !g.decode && !g.list &&
                     g.form > 1)
                     complain("warning: output will be concatenated zip files"
                              " -- %s will not be able to extract", g.prog);
-                process(strcmp(argv[n], "-") ? argv[n] : NULL);
+                process(n < nop && strcmp(argv[n], "-") == 0 ? NULL : argv[n]);
                 done++;
             }
-        option(NULL);
 
         // list stdin or compress stdin to stdout if no file names provided
         if (done == 0)