diff --git a/lib/default.nix b/lib/default.nix
index f62de95..cda082e 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -15,7 +15,9 @@ lib.makeExtensible (self:
     attrs = callLibs ./attrs.nix;
     os = callLibs ./devos;
     lists = callLibs ./lists.nix;
+    strings = callLibs ./strings.nix;
 
     inherit (attrs) mapFilterAttrs genAttrs' pathsToImportedAttrs concatAttrs;
     inherit (lists) pathsIn;
+    inherit (strings) rgxToString;
   })
diff --git a/lib/strings.nix b/lib/strings.nix
new file mode 100644
index 0000000..56a0861
--- /dev/null
+++ b/lib/strings.nix
@@ -0,0 +1,20 @@
+{ lib, ... }:
+{
+  # returns matching part of _regex_ _string_; null indicates failure.
+  rgxToString = regex: string:
+    let
+      match =
+        let
+          head = lib.substring 0 1 regex;
+          sec = lib.substring 1 2 regex;
+        in
+        if head == "^"
+          || head == "."
+          || (sec == "*" || sec == "+" || sec == "?")
+        then builtins.match "(${regex}).*" string
+        else builtins.match ".*(${regex}).*" string;
+    in
+    if lib.isList match
+    then lib.head match
+    else null;
+}
diff --git a/tests/lib.nix b/tests/lib.nix
index 249824e..65559f8 100644
--- a/tests/lib.nix
+++ b/tests/lib.nix
@@ -59,4 +59,11 @@ lib.runTests {
       f = false;
     };
   };
+
+  testRgxToString = lib.testAllTrue [
+    (rgxToString ".+x" "vxk" == "vx")
+    (rgxToString "^fo" "foo" == "fo")
+    (rgxToString "a?" "a" == "a")
+    (rgxToString "hat" "foohatbar" == "hat")
+  ];
 }