crontab bash tests

[Jon LaBadie]

On Mon, Sep 25, 2023 at 01:39:43PM +0200, lejeczek via ubuntu-users wrote:
>
>Failed to mention - it's root's cron.
>command works, both in cron & "regular" shell
>_crontab_ as such seems to work -- it;s only first bit,
>psql, which is sudoed -- but it always seems to end up with
>_false_
>Having it "simplified" - in postgres' cron, so no! sudo:
>
>*/1 * * * * [ $(psql --quiet --port=5433 -x -c 'select state
>from pg_stat_replication;' | grep streaming > /dev/null)$?
>-eq 0 ] && touch /tmp/pgSQL-5433.isMaster || rm -f
>/tmp/pgSQL-5433.isMaster
>
>still! on the systems/boxes which outside of cron, end up
>doing _rm_, in cron does the opposite, _touch_
>
>Something to do with _cron_ invokes bash in Ubuntu?
>I've been doing this for many long years in RHEL/Centos, and
>it always worked - actually the same crontab works in
>Centos... as expected.
>

May not apply here but some may not realize this potential problem.

In an if statement, ex

   if THIS
   then
      A
   else
      B
   fi

Only one of A or B will execute.  However if you use logical operators:

   THIS && A || B

both A and B could execute.  Assume THIS succeeds, A executes.  But if
A then fails, B also executes.

So in your code, if the touch executes but "fails" due to some 
permission problem the rm command will run also.

-- 
Jon H. LaBadie                  ubu at labadie.us