Add Check If Command Is Executable Before Using as a unix til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_998 TILs and counting..._
+_999 TILs and counting..._
 
 ---
 
@@ -911,6 +911,7 @@ _998 TILs and counting..._
 - [Change Default Shell For A User](unix/change-default-shell-for-a-user.md)
 - [Change To That New Directory](unix/change-to-that-new-directory.md)
 - [Check If A Port Is In Use](unix/check-if-a-port-is-in-use.md)
+- [Check If Command Is Executable Before Using](unix/check-if-command-is-executable-before-using.md)
 - [Check The Current Working Directory](unix/check-the-current-working-directory.md)
 - [Clear The Screen](unix/clear-the-screen.md)
 - [Command Line Length Limitations](unix/command-line-length-limitations.md)

unix/check-if-command-is-executable-before-using.md

@@ -0,0 +1,18 @@
+# Check If Command Is Executable Before Using
+
+When writing a quick bash script, you may want to check if a command exists and
+is executable before trying to call it. This can be done with `command`, a builtin shell command, and the `-v` flag.
+
+> If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not.
+
+Knowing that, we can redirect the output of the command to `/dev/null` and then
+short-circuit executing the command if it's not available.
+
+```bash
+command -v pbcopy >/dev/null 2>&1 && echo 'something' | pbcopy
+```
+
+In this example, I execute the `pbcopy` command, which copies text to my system
+clipboard, only if that command is available and executable.
+
+See `man bash` and find the listing for `command` for more details.