$ rustup toolchain --help
rustup.exe-toolchain
Modify or query the installed toolchains
USAGE:
    rustup.exe toolchain [SUBCOMMAND]
FLAGS:
    -h, --help    Prints help information
SUBCOMMANDS:
    list         List installed toolchains
    install      Install or update a given toolchain
    uninstall    Uninstall a toolchain
    link         Create a custom toolchain by symlinking to a directory
    help         Prints this message or the help of the given subcommand(s)
Many `rustup` commands deal with *toolchains*, a single installation
of the Rust compiler. `rustup` supports multiple
types of
toolchains. The most basic track the official release channels:
'stable', 'beta' and 'nightly'; but `rustup`
can also install
toolchains from the official archives, for alternate host platforms,
and from local builds.
Standard
release channel toolchain names have the following form:
    <channel>[-<date>][-<host>]
    <channel>       =
stable|beta|nightly|<version>
    <date>          = YYYY-MM-DD
    <host>          = <target-triple>
'channel' is
either a named release channel or an explicit version
number, such as '1.8.0'. Channel names can be optionally
appended with
an archive date, as in 'nightly-2014-12-18', in which case the
toolchain is downloaded from the archive
for that date.
Finally, the host may be specified as a target triple. This is most
useful for installing a 32-bit
compiler on a 64-bit platform, or for
installing the [MSVC-based toolchain] on Windows. For example:
    rustup
toolchain install stable-x86_64-pc-windows-msvc
For convenience, elements of the target triple that are omitted will
be
inferred, so the above could be written:
    $ rustup default stable-msvc
Toolchain names that don't name a
channel instead can be used to name
custom toolchains with the `rustup toolchain link` command.