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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 $delay let count-- echo -n "." done 
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It's nothing, these colons are part of the command names apparently. You can verify yourself by creating and running a command with : in the name. The shell by default will autoescape them and its all perfectly legal. Follow this answer to receive notifications.
Bash and sh both use colons (":") in more than one context. You'll see it used as a separator ($PATH, for example), as a modifier (${n:="foo"}) and as a null operator ("while :").
It is used when a command is needed, as in the then condition of an if command, but nothing is to be done by the command.
-d is a operator to test if the given directory exists or not. For example, I am having a only directory called /home/sureshkumar/test/. The directory variable contains the "/home/sureshkumar/test/" if [ -d $directory ]
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 Check http://wiki.bash-hackers.org/syntax/pe
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