Shell Programming and Scripting

#!/bin/sh                                                                      

echo my pid $$
echo my name $0
if ( ps -ef | grep -v grep |grep "/bin/sh $0" | grep -v $$ ) ; then
   echo somebody else is running  $$ cancelling
   exit
fi

echo me running, continuing with execution

while (true) ; do
  continue
done
<continue with script>

$ ./try.sh &
[2] 10191
my pid 10191
my name ./try.sh
me running, continuing with execution

$ ./try.sh
my pid 17374
my name ./try.sh
<username>   10191 26900 30 12:56 pts/2    00:00:01 /bin/sh ./try.sh
somebody else is running 17374 cancelling

script_name=try.sh
ps -ha | grep "$script_name" | grep -v grep