Add '$f' and '$p' expansions to 'exec' shortcut function

There are other expansions available, but I don't really think they make
sense, or why there are two of them for the same thing (`$FILE` and `%`
expand to the file name).

I added `$f` and `$p`, which expand to the document's path and current
page respectively, while keeping the other 2 just in case it breaks
someone's setup. I also documented them in both `zathura(1)` and
`zathurarc(5)`.

doc/man/zathura.1.rst

@@ -225,7 +225,8 @@ close
   Close document
 
 exec
-  Execute an external command
+  Execute an external command. ``$f`` expands to the current document path, and ``$p`` to the
+  current page number
 
 info
   Show document information

doc/man/zathurarc.5.rst

@@ -231,7 +231,8 @@ They can also be combined with modifiers:
 
   * ``exec``:
 
-    Execute an external command.
+    Execute an external command. ``$f`` expands to the current document path,
+    and ``$p`` to the current page number.
 
   * ``focus_inputbar``
 

zathura/commands.c

@@ -519,6 +519,7 @@ error_ret:
   return true;
 }
 
+
 bool
 cmd_exec(girara_session_t* session, girara_list_t* argument_list)
 {
@@ -533,18 +534,33 @@ cmd_exec(girara_session_t* session, girara_list_t* argument_list)
 
   if (zathura->document != NULL) {
     const char* path = zathura_document_get_path(zathura->document);
+    unsigned int page = zathura_document_get_current_page_number(zathura->document);
+    char page_buf[ZATHURA_PAGE_NUMBER_MAX_DIGITS];
+    snprintf(page_buf, ZATHURA_PAGE_NUMBER_MAX_DIGITS, "%d", page);
 
     GIRARA_LIST_FOREACH_BODY_WITH_ITER(argument_list, char*, iter, value,
       char* r = girara_replace_substring(value, "$FILE", path);
+      char* s = NULL;
 
       if (r != NULL) {
-        char* s = girara_replace_substring(r, "%", path);
+        s = girara_replace_substring(r, "%", path);
         g_free(r);
+        r = NULL;
+      }
 
       if (s != NULL) {
-          girara_list_iterator_set(iter, s);
+        r = girara_replace_substring(s, "$f", path);
+        g_free(s);
+        s = NULL;
       }
+
+      if (r != NULL) {
+        s = girara_replace_substring(r, "$p", page_buf);
+        g_free(r);
+        r = NULL;
       }
+
+      girara_list_iterator_set(iter, s ? s : r);
     );
   }
 

zathura/shortcuts.c

@@ -1469,6 +1469,9 @@ sc_exec(girara_session_t* session, girara_argument_t* argument, girara_event_t*
 
   if (zathura->document != NULL) {
     const char* path = zathura_document_get_path(zathura->document);
+    unsigned int page = zathura_document_get_current_page_number(zathura->document);
+    char page_buf[ZATHURA_PAGE_NUMBER_MAX_DIGITS];
+    snprintf(page_buf, ZATHURA_PAGE_NUMBER_MAX_DIGITS, "%d", page + 1);
 
     girara_argument_t new_argument = *argument;
 
@@ -1484,6 +1487,20 @@ sc_exec(girara_session_t* session, girara_argument_t* argument, girara_event_t*
       return false;
     }
 
+    r = girara_replace_substring(s, "$f", path);
+    g_free(s);
+
+    if (r == NULL) {
+      return false;
+    }
+
+    s = girara_replace_substring(r, "$p", page_buf);
+    g_free(r);
+
+    if (s == NULL) {
+      return false;
+    }
+
     new_argument.data = s;
     const bool ret = girara_sc_exec(session, &new_argument, event, t);
     g_free(s);

zathura/zathura.h

@@ -70,8 +70,11 @@ enum {
   ZOOM_SMOOTH
 };
 
-/* unspecified page number */
+/* on page numbers */
 enum {
+  /* We should never open a pdf with more that 99.999 pages... right? */
+  ZATHURA_PAGE_NUMBER_MAX_DIGITS = 5,
+  /* unspecified page numbers */
   ZATHURA_PAGE_NUMBER_UNSPECIFIED = INT_MIN
 };