You have a tool called xsparse (https://www.gnu.org/software/tar/utils/xsparse.html) that is used to expand sparse files stored in GNU tar format.
The spec given https://www.gnu.org/software/tar/manual/html_node/PAX-1.html#SEC193 Says that “The sparse map itself is stored in the file data block, preceding the actual file data. It consists of a series of octal numbers of arbitrary length, delimited by newlines.” However I think the xsparse tool interprets the number of holes, offsets and lengths as decimal rather than octal, so either 1. the tool doesn’t meet the spec 2. the spec is wrong 3. or more likely I have the wrong end of the stick 😊
