Sometimes we do want to comment or uncomment a block of lines together in VI editor. I struggle sometimes, so here are some tips.

For Uncommenting a block of text is almost the same:

Put your cursor on the first # character, press `CtrlV (or CtrlQ for gVim)`, and go down until the last commented line and press x, that will delete all the # characters vertically.

For Commenting a block of text is almost the same:

* First, go to the first line you want to comment, press `Ctrl + v`. This will put the editor in the VISUAL BLOCK mode.
* Then using the arrow key and select until the last line and Now press `Shift + I` , which will put the editor in INSERT mode.
* Then press '#' character. This will add a hash to the first line.
* Then press Esc (give it a second), and it will insert a '#' character on all other selected lines.

For the stripped-down version of vim shipped with debian/ubuntu by default, type : s/^/# in the third step instead.

Reference: Stackoverflow