After so much research, I found a simple solution for this ( I am using elementary OS), inspired by the following link.
Run the following command to open .bashrc file in edit mode. [You
may also use vi or any other editor].
~$ sudo nano ~/.bashrc
Add the following line at the end of the file and save.
export PATH="[FLUTTER_SDK_PATH]/flutter/bin:$PATH"
For Example :
export PATH="/home/rageshl/dev/flutter/bin:$PATH"
I believe this is the permanent solution for setting path in flutter in Ubuntu distro
Hope this will helpful.