add bash section

bash/script.md

@@ -0,0 +1,21 @@
+## Useful functions
+
+### Bash trap
+
+- https://tldp.org/LDP/Bash-Beginners-Guide/html/sect_12_02.html
+```bash
+# Define function called before exiting script after an error is caught.
+function set_error_status() {
+    echo "[$(date '+%Y%m%d %H%M%S')] : Something went wrong in the script, exiting." | tee -a "${LOGFILE}"
+    echo "2 vault-snapshot-restore - KO" > ${STATUSFILE}
+}
+# Set the function called when the ERR signal is caught.
+trap set_error_status ERR
+```
+
+### Exit immediatly on error and when variables are empty
+
+- https://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html
+```bash
+set -eu
+```