How can you see internal xls documents?

Question

go

xls consists of several files, but I can't get access to viewing files through standard tools and libraries known to me. The question is how to find out the names of all these files and access the contents.

Answer 1

xls (until 2007) - proprietary (without public documentation), microsoft binary format that is almost useless to work with. There is however a library https://github.com/extrame/xls (libxls rewritten in Go) that allows you to open and read binary xls files.
With the new xlsx, xlsm formats, there is more sense. This is a collection of xlm packaged in zip. Accordingly, you can unpack https://golang.org/pkg/archive/zip/ and work with xml https://golang.org/pkg/encoding/xml/ from the standard library or, for convenience, use the ready-made package https://github. com/tealeg/xlsx.
To see what is inside foo.xlsx just for fun, rename it to foo.xlsx.zip and open it with a regular archiver.