Why does tar cvpfz /tmp/backup.tgz . backup hidden files?
(Note ls . does not see the hidden files. Trivia: there are ways to see hidden files such as with ls -a but this is just trivia. The question pertains to a difference in the behaviour when similar behaviour might be expected.)
Quick answer: use ls -a to see the "hidden" files.
Long story: there's no such thing as a "hidden" file in UNIX/Linux, in the sense that the Linux kernel does not mark "hidden" files in any special way (as opposed, e.g., to what Windows does).
There is however a convention that file names starting with a dot character . are not displayed by ls unless the user explicitly asks for it (hence, the -a option). Since this was the convention adopted by the ls program (one of the first commands that existed in UNIX), it was followed by other file-display utilities, like Nautilus and the graphical file selection dialog.
On the other hand, since it's only a convention on displaying files, it does not affect other file-manipulating commands like tar.
