add trap error/exit examples

README.md

@@ -7,9 +7,20 @@ I’m coming across having to write the same shell script bits occasionally, and
 - Write once (here) and copypasta everywhere.
 - sh compatible if possible
 
+# Examples
+
+This section shows example usages for common shell patterns.
+
+## Trap errors
+
+[trap_error_example.sh](trap_error_example.sh): If you run a script with -e that produces state that you want to clean up if anything goes wrong in your script.
+
+[trap_exit_example.sh](trap_exit_example.sh): if you run a script that launches other processes, and you want to make sure those processes exit when your script exists.
 
 # Functions
 
+This section documents reusable functions for your scripts.
+
 ## `wait_for_url $url $duration $iterations`
 
 Wait for a particular URL to be available using `curl`. Wait `$duration` seconds between attempts, try `$iterations` times. Defaults to `1` seconds and `3` times.

trap_error_example.sh

@@ -0,0 +1,9 @@
+# if you run a script with -e that produces state that you want to clean up if anything goes wrong in your script, this helps:
+
+trap 'handle_error' ERR
+
+handle_error () {
+	echo "an error has occured, let’s clean up some stuff"
+	# rm some-stuff.txt
+}
+

trap_exit_example.sh

@@ -0,0 +1,3 @@
+# if you run a script that launches other processes, and you want to make sure those processes exit when your script exists, this helps:
+
+trap 'kill $(jobs -p)' EXIT