Clarify -f argument parsing

[thaliaarchi]

This clarifies the behavior of -f / --from-file in the manual and usage. It does not actually take an argument, as documented and commonly believed; it instead modifies the required filter positional argument.

Thus, the following are perfectly valid, though one might assume they are not with the previous documentation:

• jq -fn f.jq
• jq -f -n f.jq
• jq f.jq -f
• jq --args -f f.jq
• jq --args -f -- f.jq
• jq --args f.jq -f
• jq --jsonargs -f f.jq

[emanuele6]

Thank you; can you also fix exec jq --args -MRnf "$0" -- "$@" in the example script?

"$0" should go after -- so exec jq --args -MRfn -- "$0" "$@"

[thaliaarchi]

Good point. Fixed.

[01mf02]

Thank you for clarifying this; I was also under the misconception that -f takes an argument. Now I have corrected this in my alternative jq interpreter jaq 01mf02/jaq@2ab2e94. The code has even become smaller due to this change. :)