[cuu508]

In Debian cron, you can do:

0 0 */50,1-7 * FRI

It works, but it's a bit of a hack (to put it mildly ;-) )

Consider this expression:

0 0 1-7 * FRI

This one will run on dates 1-7, and additionally on every Friday. This is almost what we want, except we want an "AND" relationship between the day-of-month and the day-of-week fields, instead of the "OR" relationship.

The weird extra */50 bit exploits a quirk in Debian cron's expression parsing logic. It fools cron into thinking the day-of-month field is a wildcard field, and into applying the "AND" logic.