Either start or not a "d"

I try to get the date number format from a date format string. The date number format is - if present - either a single d or a double d. But the whole string can contain a place holder for the dayname also - ddd or dddd. How can I get the d or dd, if present?
I tried [^d](?<pattern>d{1,2})[^d] which works well with the standard German format (dddd, d. MMMM yyyy). But that fails when the daynumber comes first (say: d. dddd MMMM yyyy; here, ^(?<pattern>d{1,2})[^d] does the trick), and it fails when the daynumber comes last.
Actually I need something like a "either start of the string or not a d", i.e. ^|[^d] - but that does not work. How can that be solved?