Add a Specific Character at the Start of Each Line in a Text File Using Vi Editor

You can easily accomplish this using the command

:%s/^/#/g

to insert "#" at the start of every line. However, since you want to skip blank lines, an alternative is

:%s/^\(.\)/#\1/

which matches only lines with at least one character. This way, you ensure that no unnecessary "#" is added to empty lines, giving you precise results.

We could achieve this in multiple ways. One simple method involves visual block mode. Start by pressing Ctrl+v to select the lines, then I (capital i) to enter insert mode, type #, and press Esc to apply the change. This method is intuitive and gives us control over which lines are modified. We use it often because of its flexibility.

When you’re working in Vi, one handy trick is to use the norm command. After entering command mode, you can type

:%norm I#

to insert "#" at the start of each line. If you prefer to target only specific lines or a block, visually select the lines, then execute

:'<,'>norm I#

This approach is versatile and allows you to quickly comment out sections of code or text without affecting everything.

You can use the command

:v/^[[:blank:]]*$/ s/^/#/

to add # only to non-blank lines. This avoids blank lines by applying the substitution to lines not matching the blank line pattern.