title: What does the colon dash ":-" mean in bash
body: <p>The result is the one desired; after a bit of trial and error.  I don't understand what the "2:-" and "3:-" do/mean.  Can someone explain.</p>
  
  <pre><code>#!/bin/bash
  pid=$(ps -ef | grep java | awk ' NR ==1 {print $2}')
  
  count=${2:-30}  # defaults to 30 times
  delay=${3:-10} # defaults to 10 second
  mkdir $(date +"%y%m%d")
  folder=$(date +"%y%m%d")
  while [ $count -gt 0 ]
  do
      jstack $pid &gt;./"$folder"/jstack.$(date +%H%M%S.%N)
      sleep $delay
      let count--
      echo -n "."
  done
  </code></pre>