Escape newline when truncating notification variables

[mayrstefan]

General information

When notification variables get truncated we only see "...". The additional text "Attention: Removed remaining content because it was too long." is missing because it is in a new line. Host/Service output uses "\\n" instead of "\n". So the added text needs to escape the slash too.

Bug reports

Please include:

• Detailed steps to reproduce the bug

1. use a local check to simulate a service with very long output

#!/bin/bash
cat <<EOF
<<<local>>>
0 "longoutput" - short output\nlong output\n$(for i in {1..128000}; do echo -n "x"; done)
EOF

2. Use the example script from https://docs.checkmk.com/latest/en/notifications.html?lquery=notifications#scripts
3. change the notification script to change state
4. look into the output of the notification script

Proposed changes

Escape the slash to generate "\\n" as output