Support environment variables in the hrtf_tables config value

Alc/hrtf.c

@@ -787,22 +787,53 @@ static struct Hrtf *LoadHrtf(ALuint deviceRate)
     {
         struct Hrtf *Hrtf = NULL;
         char fname[PATH_MAX];
+        const char *next;
         ALchar magic[8];
         ALuint i;
         FILE *f;
 
+        i = 0;
         while(isspace(*fnamelist) || *fnamelist == ',')
             fnamelist++;
-        i = 0;
-        while(*fnamelist != '\0' && *fnamelist != ',')
+        next = fnamelist;
+        while(*(fnamelist=next) != '\0' && *fnamelist != ',')
         {
-            const char *next = strpbrk(fnamelist, "%,");
+            next = strpbrk(fnamelist, "%,$");
             while(fnamelist != next && *fnamelist && i < sizeof(fname))
                 fname[i++] = *(fnamelist++);
 
             if(!next || *next == ',')
                 break;
 
+            if(*next == '$')
+            {
+                next++;
+                if(*next == '$')
+                {
+                    /* '$$' becomes a single '$'. */
+                    if(i < sizeof(fname))
+                        fname[i++] = '$';
+                    next++;
+                }
+                else
+                {
+                    const char *str;
+                    char envname[1024];
+                    size_t k = 0;
+
+                    while((isalnum(*next) || *next == '_') && k < sizeof(envname)-1)
+                        envname[k++] = *(next++);
+                    envname[k++] = '\0';
+
+                    if((str=getenv(envname)) != NULL)
+                    {
+                        int wrote = snprintf(&fname[i], sizeof(fname)-i, "%s", str);
+                        i += minu(wrote, sizeof(fname)-i);
+                    }
+                }
+                continue;
+            }
+
             /* *next == '%' */
             next++;
             if(*next == 'r')
@@ -819,7 +850,6 @@ static struct Hrtf *LoadHrtf(ALuint deviceRate)
             }
             else
                 ERR("Invalid marker '%%%c'\n", *next);
-            fnamelist = next;
         }
         i = minu(i, sizeof(fname)-1);
         fname[i] = '\0';