Bug#968571: apt: print-uri and apt-helper documentation enhancements

[Johannes 'josch' Schauer]

Package: apt
Version: 2.1.10
Severity: wishlist

Hi,

some possible improvements to documentation as mentioned on IRC.

1. add more information to the --help output of apt-helper:

a) multiple things can be downloaded in the same call

17:05 < juliank> download-file [ uri target-path [hash...] ]...

b) Checksum-FileSize: or SHA256: can be added at the end

c) target is the output filename and not a directory

2. make it clear that nothing will be printed with --print-uris in case
the file that is to be downloaded already exists. Currently the docs
say "Instead of fetching the files to install their URIs are
printed". Independent of whether the resulting files already exists,
they will not get downloaded and thus my expectation from reading
this sentence is, that nothing gets downloaded with --print-uris
anyways, then their URIs are *always* printed. With the current
behavior the only reliable way to retrieve filenames is to execute
"apt-get download --print-uris" in a new and empty directory. Since
this is the *only* reliable way, maybe that information should also
be documented.

Thanks!

cheers, josch