I have followed all the command to install ros melodic in Ubuntu bionic but stucked at setting up environment variables.

edit

/otp/ros...

is this a typo in your question or what you're actually seeing it should be /opt/ros.... This could be causing your problem.

If you look at the contents of your .bashrc script you can check and fix the typo if that's the case

i copy pasted from http://wiki.ros.org/melodic/Installation/Ubuntu and it is like

echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc

Ok.

So what is the output of ls -al /opt/ros/melodic/setup.bash?

And the output of lsb_release -a?

And of uname -a?

Output of 1st ls: cannot access '/opt/ros/melodic/setup.bash' : No such file or directory 2nd No LSB modules are available. And for 3rd one.. my PC name, Ubuntu version, GNU/Linux

We need the verbatim, exact copy-paste of the uname -a output. You can change your PC name, but leave the rest.

As to the rest: it would appear that you haven't installed ROS.

unaame -a output as

Linux *********  #26~18.04.1-Ubuntu SMP Thu Jun 27 07:28:31 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

i even tried instaling LSB but it shows

E: Malformed entry 1 in list file /etc/apt/sources.list.d/ros-latest.list (Suite)
E: The list of sources could not be read.

Ah, that would appear to be your problem: it's likely that apt install ros-melodic-desktop-full didn't actually succeed. Didn't you get an error?

I'm pretty sure that the fact that lsb_release doesn't work is the cause of your problems.

What is the output of cat /etc/apt/sources.list.d/ros-latest.list?

it gives

deb http://packages.ros.org/ros/ubuntu


(lsb_release -sc) main

output of trying install ros was w/o error when i run 1st time but it gives this now

E: Malformed entry 1 in list file /etc/apt/sources.list.d/ros-latest.list (Suite)
E: The list of sources could not be read.
E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?