I couldn't find documentation (hard to search for as you might imagine). Testing it out, basically that line downloads and executes the bash script stored at https://rvm.beginrescueend.com/install/rvm . Would like to understand how it works; is it related to the $(command) expansion construct? Why not use "curl -s http://files.redsymbol.net/foo/foo.sh | bash"?
<() is a new way to do I/O redirection, by which I mean it was introduced by I think the Korn shell in the early 1990s, which explains why you haven't heard of it. Also it isn't implementable on all Unixes.
The way it works is that if you say
foo <(bar) -o >(baz) <(quuz)
foo sees them as command-line arguments, which might look like
foo /dev/fd/3 -o /dev/fd/4 /dev/fd/5
and if it is clever enough to treat them as filenames and open them, then it will get the stdout of bar, the stdin of baz, and the stdout of quux, respectively.
The way this works is that the shell opens pipes to the other command lines first, then generates filenames for them.
I did not know that you could use it with other I/O redirections such as <!
As a bonus, the <() syntax means you can pipe even to and from commands that don't read from stdin or stdout. They must not, however, depend on the ability to seek.
My most common use for this is nonlinear pipe flow, e.g.
I think the parentheses are just for grouping of the second command. The "<" means feed the stdout of the second command into the stdin of the first.
So what's happening here is the output of curl (a script) is being fed directly into a bash shell and executed. I think it's basically an awkward way of piping a command in reverse.
using only the second "<" would result in bash being called with a argument like "/dev/fd/N", which is where the output of the subshell is coming from.
The first "<" redirects the output of this file descriptor into the stdin of bash.
So both are needed, but you could just do it with a pipe :/
