api: add support of environment variables in function string_eval_expression() and command /eval (issue #388)

src/core/wee-command.c

@@ -7195,9 +7195,10 @@ command_init ()
            "  3. a color (format: \"color:xxx\")\n"
            "  4. an info (format: \"info:name,arguments\", arguments are "
            "optional)\n"
-           "  5. an option (format: \"file.section.option\")\n"
-           "  6. a local variable in buffer\n"
-           "  7. a hdata name/variable (the value is automatically converted "
+           "  5. an environment variable (format: \"env:XXX\")\n"
+           "  6. an option (format: \"file.section.option\")\n"
+           "  7. a local variable in buffer\n"
+           "  8. a hdata name/variable (the value is automatically converted "
            "to string), by default \"window\" and \"buffer\" point to current "
            "window/buffer.\n"
            "Format for hdata can be one of following:\n"
@@ -7214,6 +7215,7 @@ command_init ()
            "\n"
            "Examples (simple strings):\n"
            "  /eval -n ${info:version}                     ==> 0.4.3\n"
+           "  /eval -n ${env:HOME}                         ==> /home/user\n"
            "  /eval -n ${weechat.look.scroll_amount}       ==> 3\n"
            "  /eval -n ${window}                           ==> 0x2549aa0\n"
            "  /eval -n ${window.buffer}                    ==> 0x2549320\n"

src/core/wee-eval.c

@@ -352,7 +352,15 @@ eval_replace_vars_cb (void *data, const char *text)
         return strdup ((ptr_value) ? ptr_value : "");
     }
 
-    /* 7. option: if found, return this value */
+    /* 7. environment variable */
+    if (strncmp (text, "env:", 4) == 0)
+    {
+        ptr_value = getenv (text + 4);
+        if (ptr_value)
+            return strdup (ptr_value);
+    }
+
+    /* 8. option: if found, return this value */
     if (strncmp (text, "sec.data.", 9) == 0)
     {
         ptr_value = hashtable_get (secure_hashtable_data, text + 9);
@@ -385,7 +393,7 @@ eval_replace_vars_cb (void *data, const char *text)
         }
     }
 
-    /* 8. local variable in buffer */
+    /* 9. local variable in buffer */
     ptr_buffer = hashtable_get (pointers, "buffer");
     if (ptr_buffer)
     {
@@ -394,7 +402,7 @@ eval_replace_vars_cb (void *data, const char *text)
             return strdup (ptr_value);
     }
 
-    /* 9. hdata */
+    /* 10. hdata */
     value = NULL;
     hdata_name = NULL;
     list_name = NULL;