diff --git a/_posts/03-05-01-Command-Line-Interface.md b/_posts/03-05-01-Command-Line-Interface.md
index 2ab6df0..3371823 100644
--- a/_posts/03-05-01-Command-Line-Interface.md
+++ b/_posts/03-05-01-Command-Line-Interface.md
@@ -23,7 +23,8 @@ Let's write a simple "Hello, $name" CLI program. To try it out, create a file na
 {% highlight php %}
 <?php
 if($argc != 2) {
-    die("Usage: php hello.php [name].\n");
+    echo "Usage: php hello.php [name].\n";
+    exit(1);
 }
 $name = $argv[1];
 echo "Hello, $name\n";
@@ -31,6 +32,8 @@ echo "Hello, $name\n";
 
 PHP sets up two special variables based on the arguments your script is run with. [`$argc`][argc] is an integer variable containing the argument *count* and [`$argv`][argv] is an array variable containing each argument's *value*. The first argument is always the name of your PHP script file, in this case `hello.php`.
 
+The `exit()` expression is used with a non zero number to let the shell know that the command failed. Commonly used exit codes can be found [here][exit-codes]
+
 To run our script, above, from the command line:
 
 {% highlight bash %}
@@ -50,3 +53,4 @@ Hello, world
 [argv]: http://php.net/manual/en/reserved.variables.argv.php
 [php-cli]: http://php.net/manual/en/features.commandline.php
 [php-cli-windows]: http://www.php.net/manual/en/install.windows.commandline.php
+[exit-codes]: http://www.gsp.com/cgi-bin/man.cgi?section=3&topic=sysexits
\ No newline at end of file