check variable value when nothing is returned

Shell Programming and Scripting
1

Hi all,

I am wondering how can I check when a variable has nothing returned in it. I am trying to store a pid in this variable to see if a script is running in the background. So I am using something like that 

proc_pid=`ps -ef |grep script.sh|grep -v grep|awk '{print $2}'`
if [ $proc_pid -ne "" ]
then 
      <do something>
else
      <do something else>
fi

It seems though that this check is not exactly correct since I'm getting the following
... test: Specify a parameter with this command.
Can anyone help me find the correct checking condition?

Thanks in advance

2

Hi,

Try:

man test

if [ -z $proc_pid ]...

YMMV