Adds the ability to perform file backups before installing newer files on top
of existing ones. Adds a status message about backups to stdout if running in
verbose mode.
The '--backup' option would previously accept arguments separated from the
option either by a space or an equals sign. The GNU implementation strictly
requires an "equals" for argument separation.
As the argument to '--backup' is optional, the equals sign mustn't be ommited
as otherwise there is no way to tell a file argument apart from an argument
that's meant for the '--backup' option. This ensures that if '--backup' is
present it either has no further associated arguments (i.e. fallback to the
default), or the arguments are separated by an equals sign.
The '-d' flag should create all ancestors (or components) of a
directory regardless of the presence of the "-D" flag.
From the man page:
-d, --directory
treat all arguments as directory names; create all components of the specified directories
With GNU:
$ install -v -d dir1/di2
install: creating directory 'dir1'
install: creating directory 'dir1/di2'
With this version:
$ ./target/release/install -v -d dir3/di4
install: dir3/di4: No such file or directory (os error 2)
install: dir3/di4: chmod failed with error No such file or directory (os error 2)
install: created directory 'dir3/di4'
Also, one of the unit tests misinterprets what a "component" is,
and hence was fixed.
Also don't run chmod when we just failed to create the directory.
Behaviour before this patch:
$ ./target/release/install -v -d dir1/dir2
install: dir1/dir2: Permission denied (os error 13)
install: dir1/dir2: chmod failed with error No such file or directory (os error 2)
install: created directory 'dir1/dir2'
* install: implement `-C` / `--compare`
GNU coreutils [1] checks the following: whether
- either file is nonexistent,
- there's a sticky bit or set[ug]id bit in play,
- either file isn't a regular file,
- the sizes of both files mismatch,
- the destination file's owner differs from intended, or
- the contents of both files mismatch.
[1] https://git.savannah.gnu.org/cgit/coreutils.git/tree/src/install.c?h=v8.32#n174
* Add test: non-regular files
* Forgot a #[test]
* Give up on non-regular file test
* `cargo fmt` install.rs
