default val arg for getenv, add extreplace for extension subst

example/obuild.cfg

@@ -1,11 +1,6 @@
-CC = (getenv CC)
-if (=s $CC "") [
-    CC = "cc"
-]
+CC = (getenv CC cc)
 
-rule default test
-
-OBJ = (strreplace (glob "*.c") ".c" ".o")
+OBJ = (extreplace (glob *.c) .c .o)
 
 rule test $OBJ [
     echo " LD" $target
@@ -36,4 +31,8 @@ action test_invoke [
 
 depend foo.o foo.h
 depend bar.o bar.h
-depend test.o [foo.h bar.h]
+depend test.o [foo.h bar.h]
+
+// default rule
+
+rule default test

globs.cc

@@ -159,4 +159,27 @@ void cs_register_globs(cscript::CsState &cs) {
         auto fnames = cscript::util::list_explode(lst);
         cs.result->set_str(ob_expand_globs(fnames).disown());
     });
+
+    cs.add_command("extreplace", "sss", [](cscript::CsState &cs,
+                                           const char *lst,
+                                           const char *oldext,
+                                           const char *newext) {
+        String ret;
+        if (oldext[0] == '.') ++oldext;
+        if (newext[0] == '.') ++newext;
+        auto fnames = cscript::util::list_explode(lst);
+        for (ConstCharRange it: fnames.iter()) {
+            if (!ret.empty()) ret += ' ';
+            auto dot = ostd::find_last(it, '.');
+            if (!dot.empty() && ((dot + 1) == oldext)) {
+                ret += ostd::slice_until(it, dot);
+                ret += '.';
+                ret += newext;
+            } else {
+                ret += it;
+            }
+        }
+        cs.result->set_str(ret.iter());
+        ret.disown();
+    });
 }

main.cc

@@ -438,16 +438,20 @@ int main(int argc, char **argv) {
         ((ObState &)cs).rule_add(file, deps, nullptr);
     });
 
-    os.cs.add_commandn("getenv", "s", [](CsState &cs, TvalRange args) {
+    os.cs.add_commandn("getenv", "ss", [](CsState &cs, TvalRange args) {
         if (((ObState &)cs).ignore_env) {
             cs.result->set_cstr("");
             return;
         }
         auto ret = ob_get_env(args[0].get_str());
-        if (ret.empty())
-            cs.result->set_cstr("");
-        else
+        if (ret.empty()) {
+            if (!args[1].get_str().empty())
+                cs.result->set_str_dup(args[1].get_str());
+            else
+                cs.result->set_cstr("");
+        } else {
             cs.result->set_str_dup(ret);
+        }
     });
 
     os.cs.add_command("invoke", "s", [](CsState &cs, const char *name) {