Bash or-equals ||= like Ruby

You can set your prompt to be the working directory with this:

PS1='\w '   # Using \W will provide just basename

Another solution (which is more akin to Ruby's or-equals in my opinion) would be:

[ -n $PWD ] || PWD=`pwd`

Bash allows for default values:

a=${b-`pwd`}

If $b is undefined, then pwd is used instead in assigning $a.

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