Hints

[...]	allowed symbols
{x}	x repetitions of symbols
*	any sequence of symbols

Country	Pattern
all	*
at	[0-9]{4}
au	[0-9]{4}
be	[0-9]{4}
bg	[0-9]{4}
ch	[0-9]{4}
cy	[0-9]{4}
cz	[0-9]{5}
de	[0-9]{5}
dk	[0-9]{4}
ee	[0-9]{5}
es	[0-9]{5}
fi	[0-9]{5}
fr	[0-9]{5}
gb	[A-Z]{1,2}[0-9]{1}[0-9A-Z]{0,1}[ ]{1}[0-9]{1}[A-Z]{2}
gr	[0-9]{5}
hr	[0-9]{5}
hu	[0-9]{4}
ie	*
is	[0-9]{3}
it	[0-9]{5}
lt	[0-9]{5}
lu	[0-9]{4}
lv	[0-9]{4}
me	[0-9]{5}
mk	[0-9]{4}
mt	[A-Z]{3}[ ]{1}[0-9]{4}
nl	[0-9]{4}[ ]{1}[A-Z]{2}
no	[0-9]{4}
nz	[0-9]{4}
pl	[0-9]{2}[-,]{1}[0-9]{3}
pt	[0-9]{4}[-]{1}[0-9]{3}
ro	[0-9]{6}
ru	[0-9]{6}
se	[0-9]{3}[ ]{1}[0-9]{2}
si	[0-9]{4}
sk	[0-9]{5}
tr	[0-9]{5}
ua	[0-9]{5}
us	[0-9]{5}
default	[0-9A-Z]{6}