Search path for .lib and .include has been enhanced to read complete

or partial paths from an environmental variable. The env variable
name has to start with '$' as the first character after the .inc
or .lib token. It is read until it hits a directory separator '/' or '\\',
or if none is found, until the end of the line. In this case the filename
has to be included in the env variable.

If the env variable is read successfully, a ngspice variable with
the same name (without leading '$') and contents is defined for
use in a .control section.

src/frontend/inpcom.c

@@ -122,7 +122,7 @@ static bool has_if = FALSE; /* if we have an .if ... .endif pair */
 static char *readline(FILE *fd);
 int get_number_terminals(char *c);
 static void inp_stripcomments_deck(struct card *deck, bool cs);
-static void inp_stripcomments_line(char *s, bool cs);
+static void inp_stripcomments_line(char *s, bool cs, bool inc);
 static void inp_fix_for_numparam(
         struct names *subckt_w_params, struct card *deck);
 static void inp_remove_excess_ws(struct card *deck);
@@ -1417,7 +1417,7 @@ static struct inp_read_t inp_read(FILE* fp, int call_depth, const char* dir_name
 
             struct card* newcard;
 
-            inp_stripcomments_line(buffer, FALSE);
+            inp_stripcomments_line(buffer, FALSE, TRUE);
 
             s = skip_non_ws(buffer); /* advance past non-space chars */
 
@@ -1952,6 +1952,47 @@ static char *inp_pathresolve_at(const char *name, const char *dir)
         return inp_pathresolve(name);
     }
 
+    /* this might contain an environmental variable at the front of the string */
+    if (name[0] == '$') {
+        char* s, *tmpnam, *tmpcurr;
+        tmpcurr = tmpnam = copy(name);
+        /* extract env variable, add rest of token to its contents */
+        char *envvar = gettok_char(&tmpcurr, '\\', FALSE, FALSE);
+        if (envvar) {
+            s = getenv(envvar + 1);/* skip '$' */
+            if (s) {
+                cp_vset(s, CP_STRING, envvar + 1);
+                char* newname = tprintf("%s%s", s, tmpcurr);
+                char* const r = inp_pathresolve(newname);
+                tfree(newname);
+                return r;
+            }
+        } else {
+            tmpcurr = tmpnam;
+            envvar = gettok_char(&tmpcurr, '/', FALSE, FALSE);
+        }
+        if (envvar) {
+            s = getenv(envvar + 1);/* skip '$' */
+            if (s) {
+                cp_vset(s, CP_STRING, envvar + 1);
+                char* newname = tprintf("%s%s", s, tmpcurr);
+                char* const r = inp_pathresolve(newname);
+                tfree(newname);
+                return r;
+            }
+        /* no directory separator found, just use the env entry (must include file name) */
+        } else {
+            envvar = tmpnam;
+            s = getenv(envvar + 1);/* skip '$' */
+            if (s) {
+                cp_vset(s, CP_STRING, envvar + 1);
+                char* const r = inp_pathresolve(s);
+                return r;
+            }
+            tfree(envvar);
+        }
+    }
+
     if (name[0] == '~' && name[1] == '/') {
         char * const y = cp_tildexpand(name);
         if (y) {
@@ -3239,7 +3280,7 @@ static void inp_stripcomments_deck(struct card *c, bool cf)
             found_control = TRUE;
         if (ciprefix(".endc", c->line))
             found_control = FALSE;
-        inp_stripcomments_line(c->line, found_control | cf);
+        inp_stripcomments_line(c->line, found_control | cf, FALSE);
     }
 }
 
@@ -3267,7 +3308,7 @@ static void inp_stripcomments_deck(struct card *c, bool cf)
  character, not as end-of-line comment delimiter, except for that it is
  located at the beginning of a line. If inside of a control section,
  still '$ ' is read a an end-of-line comment delimiter.*/
-static void inp_stripcomments_line(char *s, bool cs)
+static void inp_stripcomments_line(char *s, bool cs, bool inc)
 {
     char c = ' '; /* anything other than a comment character */
     char *d = s;
@@ -3280,6 +3321,12 @@ static void inp_stripcomments_line(char *s, bool cs)
         return;
     }
 
+    if (inc) {
+        d = nexttok(d);
+        if (*d == '$')
+            d = nexttok(d);
+    }
+
     /* Look for comments in body of line. */
     while ((c = *d) != '\0') {
         d++;