With bash putting a command in <() uses the output of the command as though it were a file. I use it to diff the output of two commands: diff <(command 1) <(command 2)

I've never used it, but I assume >() uses a command as though it were a writable file. So instead of history -a file writing to file, he does history -a >(logger) to write to the logger command. Seems pretty clever to me.

Yup, that's what it does. Shortly speaking <() or >() in bash that creates a temporary pipe.

It's called process substitution. In this case it runs the logger command, connects its input to a file in /dev/fd, and places the name of that file in the argument list of history. I've included a small demonstration below. This is useful since the history command won't write to standard out so you can't use a normal pipe. It's more common to see process substitution used to gather output from multiple commands, see http://www.linuxjournal.com/content/shell-process-redirectio...

    $ cat writer.sh 
    #!/bin/bash
    if [[ "$#" == 1 ]]; then
        echo "Wrote to file named $1" > "$1"
    else
        echo "Wrote to stdout"
    fi

    $ ./writer.sh 
    Wrote to stdout

    $ ./writer.sh | cat
    Wrote to stdout

    $ ./writer.sh >(cat)
    Wrote to file named /dev/fd/63

It appends the "new" history lines to a $HISTFILE by default, unless other file is specified.

Thanks, that's what I was missing: -a can have a file. Cool stuff and thanks to all for explaining it. http://unixhelp.ed.ac.uk/CGI/man-cgi?history does not mention the command line argument, http://linux.die.net/man/1/bash does.

You're welcome, it took me a bit of time to come up with this idea, of course, it's not perfect, but does the job pretty well.