Question

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What does it mean “bash < <( curl rvm.io/releases/rvm-install-head )”

I’m working to install Ruby on Rails on Mac OS X lion and came across several tutorials which called on this line:

bash < <(curl -s https://rvm.io/install/rvm)

I don’t know what the bash < < bit is for.

What does this line do?

Thanks

Answer 1

The first < redirects the file on the right side to the stdin of the command on the left side.

The <(...) syntax runs the command specified, saving its output to a named pipe (a special kind of file that outputs whatever is written into it without saving it to the disk) and replaces the whole <(...) with the name of the file. This is called process substitution (you can look it up in man bash) and it is used whenever a file would be needed but you want to use the output of a command instead.

As for curl, it is a command which downloads the URL given to it as argument, and outputs it to the screen (stdout).

In summary, what the command you gave does is:

1. Runs bash, giving it as input the contents of a temporary named pipe.
2. Downloads the URL https://rvm.io/install/rvm, which is a bash script, and saves it to the temporary named pipe given as input to bash.

This effectively runs the script at the URL with bash.