script bash can't get difference in $PS1 or $- when running interactivelly or via cron

Question

I want my cron scripts being executed verbosly when run interactively by a system user (for debug purpose for instance) and quietly otherwise (for cron, as I want receive e-mail if and only if I get errors).

I have tried this in my script:

case "$-" in
*i*) echo "this shell is interactive" > /tmp/log;
*) echo "this shell isn't" > /tmp/log;
esac

but even when run interactively (/bin/bash /tmp/my_script.sh) it returns always "this shell isn't" and

echo $-

in shell script returns hB and not hiB.

I have also tried

if [ -z $PS1 ]

thinking that cron does not have $PS1 set, but once again, from prompt, echo $PS1 returns this variable, and interactively in a script, it returns nothing :/

I would like to know why interactively (/bin/bash my_script.sh) this does not return the i value for $- nor the value of $PS1.

Many thanks for your help!

Answer 1

You could check if stdin is a tty.

Alternatively you could add a flag to your script telling it to be quiet or verbose instead of making it guess.

Answer 2

You could set an environment variable in cron, and check for that.

Put THISISCRON=1 on a line on its own above the cron entry.

Answer 3

Bash scripts never have interactive option on. They are non-interactive everywhere.