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Editorial Team
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Asked: 2026-05-31T12:32:03+00:00

This command works fine: $ bash -s stable < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer) However, I

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This command works fine:

$ bash -s stable < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer)

However, I don’t understand how exactly stable is passed as a parameter to the shell script that is downloaded by curl. That’s the reason why I fail to achieve the same functionality from within my own shell script – it gives me ./foo.sh: 2: Syntax error: redirection unexpected:

$ cat foo.sh 
#!/bin/sh
bash -s stable < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer)

So, the questions are: how exactly this stable param gets to the script, why are there two redirects in this command, and how do I change this command to make it work inside my script?

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1 Answer

  1. Editorial Team

    Regarding the “redirection unexpected” error:

    That’s not related to stable, it’s related to your script using /bin/sh, not bash. The <() syntax is unavailable in POSIX shells, which includes bash when invoked as /bin/sh (in which case it turns off nonstandard functionality for compatibility reasons).

    Make your shebang line #!/bin/bash.

    Understanding the < <() idiom:

    To be clear about what’s going on — <() is replaced with a filename which refers to the output of the command which it runs; on Linux, this is typically a /dev/fd/## type filename. Running < <(command), then, is taking that file and directing it to your stdin… which is pretty close the behavior of a pipe.

    To understand why this idiom is useful, compare this:

    read foo < <(echo "bar")
echo "$foo"

    to this:

    echo "bar" | read foo
echo "$foo"

    The former works, because the read is executed by the same shell that later echoes the result. The latter does not, because the read is run in a subshell that was created just to set up the pipeline and then destroyed, so the variable is no longer present for the subsequent echo.

    Understanding bash -s stable:

    bash -s indicates that the script to run will come in on stdin. All arguments, then, are fed to the script in the $@ array ($1, $2, etc), so stable becomes $1 when the script fed in on stdin is run.

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