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.
#!/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 $pid >./"$folder"/jstack.$(date +%H%M%S.%N)
sleep $delay
let count--
echo -n "."
done
It's a parameter expansion, it means if the third argument is null or unset, replace it with what's after :-
$ x=
$ echo ${x:-1}
1
$ echo $x
$
There's also another similar PE that assign the value if the variable is null:
$ x=
$ echo ${x:=1}
1
$ echo $x
1