Replace all occurrences of a word with another

1. From the command line, %s/find_word/replacement_word/g

Re-format text blocks to wrap to a fixed character width

1. Set the text width in characters :set textwidth=80
2. Select the lines of text you want to re-format v to use visual selection
3. Reformat gq
4. To reformat a single paragraph without selecting it first {gq}

Turn on (or off) line numbering

1. To turn on line numbering, at the : prompt type set number
2. To turn off line numbering, type the command set nonumber
3. To set relative line numbers set relativenumber

Insert a comment character as the first character in a sequence of lines (i.e., comment a block)

1. Position the cursor on the first character in the first line to be commented
2. Press Ctrl-V to enter VISUAL BLOCK mode
3. Use arrow keys to select the first character in each line until the last line in sequence
4. Press Shift-I (the i key), which will put the editor in INSERT mode
5. Press #, the character to be inserted at the start of each line, note that it will not yet appear on screen
6. Press Esc (wait a couple of seconds), the # character will appear at the start of each line

Remove comment characters from multiple lines

1. Assuming # is the comment character, put your cursor on the first # character, press Ctrl-V
2. Use arrow keys to go down until the last commented line, the first character in each line should be highlighted
3. Press x to delete all the selected # characters

Delete white space on the left or beginning of a line

1. Position the cursor anywhere on the line to be editted
2. Enter the command :left
3. Any spaces before the first non-space character will be deleted moving the line to the left

Insert or remove a comment characters

1. Move the cursor to the first character of the first line you want to comment
2. Press Ctrl + V to enter Visual Block mode
3. Use the Down Arrow key to highlight down to the last line
4. Press Shift + I (uppercase I) to enter block insert mode
5. Type your comment character (e.g., # for Python/Bash, // for C++/JavaScript)
6. Press Esc
7. Wait a second—the comment characters will automatically populate across all selected lines
8. To uncomment: Press Ctrl + V, select the comment characters using the arrow keys, press x to delete them