Add Check If The First Argument Is Given as a shell til

Author: jbranchaud

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_950 TILs and counting..._
+_951 TILs and counting..._
 
 ---
 
@@ -41,6 +41,7 @@ _950 TILs and counting..._
 * [React Testing Library](#react-testing-library)
 * [ReasonML](#reasonml)
 * [Ruby](#ruby)
+* [Shell](#shell)
 * [tmux](#tmux)
 * [Unix](#unix)
 * [Vim](#vim)
@@ -819,6 +820,10 @@ _950 TILs and counting..._
 - [Wrap Things In An Array, Even Hashes](ruby/wrap-things-in-an-array-even-hashes.md)
 - [Zero Padding](ruby/zero-padding.md)
 
+### Shell
+
+- [Check If The First Argument Is Given](shell/check-if-the-first-argument-is-given.md)
+
 ### tmux
 
 - [Adjusting Window Pane Size](tmux/adjusting-window-pane-size.md)

shell/check-if-the-first-argument-is-given.md

@@ -0,0 +1,19 @@
+# Check If The First Argument Is Given
+
+In a shell script, you may want to check if an argument was given. Each
+argument is referenced numerically with the `$` prefix, so the first argument
+is `$1`. To check if the first argument is given, you can use the `-z` check.
+
+```bash
+if [ -z "$1" ]
+  then
+    echo "The first argument is missing"
+    exit 1
+fi
+```
+
+The `-z` checks if the argument is a zero-length string (so `""` or undefined
+will be true). If it is missing, then we echo out a message and exit the
+script. This is how I might fashion a script that requires the first argument.
+
+[source](https://stackoverflow.com/questions/6482377/check-existence-of-input-argument-in-a-bash-shell-script)