Add Grep For Files Without A Match as a unix til.

README.md

@@ -265,6 +265,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [File Type Info With File](unix/file-type-info-with-file.md)
 - [Find Newer Files](unix/find-newer-files.md)
 - [Global Substitution On The Previous Command](unix/global-substitution-on-the-previous-command.md)
+- [Grep For Files Without A Match](unix/grep-for-files-without-a-match.md)
 - [Hexdump A Compiled File](unix/hexdump-a-compiled-file.md)
 - [Kill Everything Running On A Certain Port](unix/kill-everything-running-on-a-certain-port.md)
 - [Killing A Frozen SSH Session](unix/killing-a-frozen-ssh-session.md)

unix/grep-for-files-without-a-match.md

@@ -0,0 +1,14 @@
+# Grep For Files Without A Match
+
+The `grep` command is generally used to find files whose contents match a
+pattern. With the `-L` (`--files-without-match`) flag, `grep` can be used to
+find files that don't match the given pattern.
+
+For instance, to find files in the current directory that don't have
+`foobar` anywhere in their content, run:
+
+```bash
+$ grep -L "foobar" ./*
+```
+
+[source](http://stackoverflow.com/questions/1748129/using-grep-to-find-files-that-dont-contain-a-given-string-pattern)