docs: update

README.md

@@ -24,6 +24,7 @@ list, send a pull request!
 * [Get the current date using `strftime`.](#get-the-current-date-using-strftime)
 * [Get the first N lines in a file.](#get-the-first-n-lines-in-a-file)
 * [Get the last N lines in a file.](#get-the-last-n-lines-in-a-file)
+* [Get the number of lines in a file.](#get-the-number-of-lines-in-a-file)
 * [Get the directory name of a file path.](#get-the-directory-name-of-a-file-path)
 * [Convert a hex color to RGB](#convert-a-hex-color-to-rgb)
 * [Convert an RGB color to hex.](#convert-an-rgb-color-to-hex)
@@ -93,6 +94,20 @@ tail() {
 }
 ```
 
+## Get the number of lines in a file.
+
+Alternative to `wc -l`.
+
+**NOTE:** Requires `bash` 4+
+
+```sh
+lines() {
+    # Usage lines "file"
+    mapfile -tn 0 lines < "$1"
+    printf '%s\n' "${#lines[@]}"
+}
+```
+
 ## Get the directory name of a file path.
 
 Alternative to the `dirname` command.