Add Get Matching Filenames As Output From Grep as a unix til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_760 TILs and counting..._
+_761 TILs and counting..._
 
 ---
 
@@ -687,6 +687,7 @@ _760 TILs and counting..._
 - [File Type Info With File](unix/file-type-info-with-file.md)
 - [Find Newer Files](unix/find-newer-files.md)
 - [Forward Multiple Ports Over SSH](unix/forward-multiple-ports-over-ssh.md)
+- [Get Matching Filenames As Output From Grep](unix/get-matching-filenames-as-output-from-grep.md)
 - [Get The Unix Timestamp](unix/get-the-unix-timestamp.md)
 - [Global Substitution On The Previous Command](unix/global-substitution-on-the-previous-command.md)
 - [Globbing For All Directories In Zsh](unix/globbing-for-all-directories-in-zsh.md)

unix/get-matching-filenames-as-output-from-grep.md

@@ -0,0 +1,21 @@
+# Get Matching Filenames As Output From Grep
+
+Standard use of the [`grep`
+command](http://man7.org/linux/man-pages/man1/grep.1.html) outputs the lines
+that match the specified pattern. You can instead output just the names of
+the files where those matches occur. To do this, include the `-l` flag.
+
+```bash
+$ grep -Rl hashrocket .
+./elixir/run-exunit-tests-in-a-deterministic-order.md
+./git/show-file-diffs-when-viewing-git-log.md
+./git/single-key-presses-in-interactive-mode.md
+./internet/enable-keyboard-shortcuts-in-gmail.md
+...
+```
+
+This recursive grep finds all the files where `hashrocket` appears. It only
+looks for the first match in a file, so each file will only be listed once
+even if there may have been multiple matches.
+
+See `man grep` for more details.