Introduce EnvSubst()

src/string.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008-2015 Kim Woelders
+ * Copyright (C) 2008-2022 Kim Woelders
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to
@@ -70,3 +70,53 @@ Estrcasestr(const char *haystack, const char *needle)
    return NULL;
 }
 #endif
+
+/*
+ * Substitute $ENV_VAR and ${ENV_VAR} with the environment variable
+ * from str into bptr[blen].
+ */
+void
+EnvSubst(const char *str, char *bptr, unsigned int blen)
+{
+   char                env[128];
+   int                 nw, len;
+   const char         *si, *p1, *p2;
+
+   for (si = str, nw = 0;; si = p2)
+     {
+	p1 = strchr(si, '$');
+	if (!p1)
+	  {
+	     nw += snprintf(bptr + nw, blen - nw, "%s", si);
+	     break;
+	  }
+	len = p1 - si;
+	nw += snprintf(bptr + nw, blen - nw, "%.*s", len, si);
+	p1 += 1;
+	p2 = *p1 == '{' ? p1 + 1 : p1;
+	/* $ENV_VAR - Name is validted */
+	for (; *p2 != '\0'; p2++)
+	  {
+	     if (!(isalnum(*p2) || *p2 == '_'))
+		break;
+	  }
+	len = p2 - p1;
+	if (*p1 == '{')
+	  {
+	     if (*p2 != '}')
+	       {
+		  p2 = p1;
+		  continue;
+	       }
+	     p1 += 1;
+	     p2 += 1;
+	     len -= 1;
+	  }
+	if (len <= 0)
+	   continue;
+	snprintf(env, sizeof(env), "%.*s", len, p1);
+	p1 = getenv(env);
+	if (p1)
+	   nw += snprintf(bptr + nw, blen - nw, "%s", p1);
+     }
+}

src/util.h

@@ -118,6 +118,9 @@ void                Esetenv(const char *name, const char *value);
 /* misc.c */
 void __PRINTF__     Eprintf(const char *fmt, ...);
 
+/* string.c */
+void                EnvSubst(const char *str, char *bptr, unsigned int blen);
+
 #define Evsnprintf vsnprintf
 #define Esnprintf snprintf