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Thread: What does this do in bash: ${pid:-}
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Old 10-12-2008
mindOnMy$ mindOnMy$ is offline
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Join Date: Oct 2008
Posts: 2
Question What does this do in bash: ${pid:-}
As i understand it, this means
if pid is
a) unset, or
b) set to null
then replace with the value on the right of the minus sign--which is null

This confuses me because
a) I thought if a variable isn't set to anything it's automatically null. If not then what is an uninitiated variable set to?
b) if the variable is already set to null, then why replace it with another null?

I see this on line 74 in the file /lib/lsb/init-functions (I'm using hardy heron ubuntu)
Here's an excerpt from the file:
Code:
if [ -z "${pidfile:-}" ]; then 
    pidfile=/var/run/${1##*/}.pid 
fi