Shell Programming and Scripting

Hello!
i have a llittle missunderstanding with a script and maybe you can explain where is the mistake.
in the first place a have this script that is working just fine

...
read -p "enter the name of the instance: " instance
while [ -z "$instance" -o -z "`cat /home/oracle/instanta | grep "$instance"`" ];
....
but if i change the second condition with -z "`grep "$instance" /home/oracle/instanta `" then the script will fail! i don't understand why because if a run both conditions in the comand line i get the same result!

the same happens with the first condition : if a change with -z "`echo "$instance`"" the script won't work

what is a little bit strange is that if i create the script with a decisional block, something like this :

if [ -z `echo $instance` ];


....

its working just fine!
i'm really confused

thank you all in advance!

echo will still output a newline even if it has a blank argument:

Code:

 $ echo $ABC123 | od -c
0000000  \n
0000001

Not really sure about the grep + cat issue does it also occur if you use $() instead of backticks? eg -z "$(grep "$instance" /home/oracle/instanta)"

Paste the output of bash -x <your script>
That might give some thing...
BTW, both works fine for me...

--ahamed