regex - this element can exist between n and m times

Example:

egrep -r '0{3,5}' /etc

Output:

/etc/login.defs:UID_MIN			 1000
/etc/login.defs:UID_MAX			60000
/etc/login.defs:SUB_UID_MIN		   100000
/etc/login.defs:SUB_UID_MAX		600100000
/etc/login.defs:GID_MIN			 1000
/etc/login.defs:GID_MAX			60000
/etc/login.defs:SUB_GID_MIN		   100000
/etc/login.defs:SUB_GID_MAX		600100000