Add Grep For Files With Multiple Matches as a unix til

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.