bash: check command exists

~/Bash/command_exists.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+if ! [ -x "$(command -v git)" ]; then
+    echo 'Error: git is not installed.' >&2
+    exit 1
+fi
+
+if ! command -v crystal &> /dev/null
+then
+    echo "<the_command> could not be found"
+    exit
+fi