diff --git a/mod/str.c b/mod/str.c
index 6d0ef7f..bfe4a40 100644
--- a/mod/str.c
+++ b/mod/str.c
@@ -122,12 +122,54 @@ static hcl_pfrc_t pf_str_length (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 	return HCL_PF_SUCCESS;
 }
 
+static hcl_pfrc_t pf_str_substr (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
+{
+	hcl_oop_t str, substr, a1, a2;
+	hcl_ooi_t size;
+	hcl_ooi_t pos;
+	hcl_ooi_t len;
+
+	str = HCL_STACK_GETARG(hcl, nargs, 0);
+	a1 = HCL_STACK_GETARG(hcl, nargs, 1);
+	a2 = HCL_STACK_GETARG(hcl, nargs, 2);
+
+	if (!HCL_IS_STRING(hcl, str))
+	{
+		hcl_seterrbfmt (hcl, HCL_EINVAL, "parameter not string - %O", str);
+		return HCL_PF_FAILURE;
+	}
+	if (!HCL_OOP_IS_SMOOI(a1))
+	{
+		hcl_seterrbfmt (hcl, HCL_EINVAL, "position not numeric - %O", a1);
+		return HCL_PF_FAILURE;
+	}
+	if (!HCL_OOP_IS_SMOOI(a2))
+	{
+		hcl_seterrbfmt (hcl, HCL_EINVAL, "length not string - %O", a2);
+		return HCL_PF_FAILURE;
+	}
+
+	size = HCL_OBJ_GET_SIZE(str);
+	pos = HCL_OOP_TO_SMOOI(a1);
+	len = HCL_OOP_TO_SMOOI(a2);
+
+	if (pos < 0) pos = 0;
+	else if (pos >= size) pos = size;
+	if (len >= size - pos) len = size - pos;
+	substr = hcl_makestring(hcl, HCL_OBJ_GET_CHAR_PTR(str, pos), len, 0);
+	if (HCL_UNLIKELY(!substr)) return HCL_PF_FAILURE;
+
+	HCL_STACK_SETRET (hcl, nargs, substr);
+	return HCL_PF_SUCCESS;
+}
+
 static hcl_pfinfo_t pfinfos[] =
 {
 	/*{ { 'V','A','R','\0' },                  { HCL_PFBASE_VAR,  HCL_NULL,           0,  0 } },*/
 	{ { 'a','t','\0' },                      { HCL_PFBASE_FUNC,  pf_str_at,         2,  2 } },
 	{ { 'a','t','P','u','t','\0' },          { HCL_PFBASE_FUNC,  pf_str_at_put,     3,  3 } },
-	{ { 'l','e','n','g','t','h','\0' },      { HCL_PFBASE_FUNC,  pf_str_length,     1,  1 } }
+	{ { 'l','e','n','g','t','h','\0' },      { HCL_PFBASE_FUNC,  pf_str_length,     1,  1 } },
+	{ { 's','u','b','s','t','r'},            { HCL_PFBASE_FUNC,  pf_str_substr,     3,  3 } }
 };
 
 /* ------------------------------------------------------------------------ */