Add Grep For Files With Multiple Matches 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/).
 
-_698 TILs and counting..._
+_699 TILs and counting..._
 
 ---
 
@@ -634,6 +634,7 @@ _698 TILs and counting..._
 - [Globbing For All Directories In Zsh](unix/globbing-for-all-directories-in-zsh.md)
 - [Globbing For Filenames In Zsh](unix/globbing-for-filenames-in-zsh.md)
 - [Grep For Files Without A Match](unix/grep-for-files-without-a-match.md)
+- [Grep For Files With Multiple Matches](unix/grep-for-files-with-multiple-matches.md)
 - [Grep For Multiple Patterns](unix/grep-for-multiple-patterns.md)
 - [Hexdump A Compiled File](unix/hexdump-a-compiled-file.md)
 - [Jump To The Ends Of Your Shell History](unix/jump-to-the-ends-of-your-shell-history.md)

unix/grep-for-files-with-multiple-matches.md

@@ -0,0 +1,31 @@
+# Grep For Files With Multiple Matches
+
+The `grep` utility is a great way to find files that contain a certain
+pattern:
+
+```bash
+$ grep -r ".class-name" src/css/
+```
+
+This will recursively look through all the files in your css directory to
+find matches of `.class-name`.
+
+Often times these kinds of searches can turn up too many results and you'll
+want to pare it back by providing some additional context.
+
+For instance, we may only want results where `@media only screen` also
+appears, but on a different line. To do this, we need to chain a series of
+`greps` together.
+
+```bash
+$ grep -rl "@media only screen" src/css |
+    xargs grep -l ".class-name"
+```
+
+This will produce a list of filenames (hence the `-l` flag) that contain
+both a line with `@media only screen` and a line with `.class-name`.
+
+If you need to, chain more `grep` commands on to narrow things down even
+farther.
+
+See `man grep` for more details.