I want to setup a simple pre hook in Bitbucket that simply checks that there's a JIRA number in commit message. When I attempt to save it, I get a message that I should enter a valid JQL query to match the desired issues.
How can I write this query to match ANY issue?
Can you please provide the JQL Query you are providing? If you want to get "All" Issues you can simply give a created > 0 or project = "Proj", either of which would catch all of your tickets. You could then use this to loop through your commit message and check your Jira Key (i.e. Proj-####) as a loop. I might also recommend on the Bitbucket you have a regex check whick looks for that specific pattern on your prehook, depending on how you write it.
Although, if you have configured it correctly it might actually be able to do it automatically. Check the documents here: https://support.atlassian.com/jira-software-cloud/docs/reference-issues-in-your-development-work/