How can I delete multiple lines in vi?

Commands listed for use in normal mode (prefix with : for command mode).
Tested in Vim.

By line amount:

• numdd - will delete num lines DOWN starting count from current cursor position (e.g. 5dd will delete current line and 4 lines under it => deletes current line and (num-1) lines under it)
• numdk - will delete num lines UP from current line and current line itself (e.g. 3dk will delete current line and 3 lines above it => deletes current line and num lines above it)

By line numbers:

• dnumG - will delete lines from current line (inclusive) UP to line number num (inclusive) (e.g. if cursor is currently on line 5 d2G will delete lines 2-5 inclusive)
• dnumgg - will delete lines from current line (inclusive) DOWN to the line number num (inclusive) (e.g. if cursor is currently on line 2 d6gg will delete lines 2-6 inclusive)
• (command mode only) :num1,num2d - will delete lines line number num1 (inclusive) DOWN to the line number num2 (inclusive). Note: if num1 is greater than num2 — vim will react with Backwards range given, OK to swap (y/n)?

I find this easier

1. Go VISUAL mode Shift+v
2. Select lines
3. d to delete

https://superuser.com/questions/170795/how-can-i-select-and-delete-lines-of-text-in-vi

Sounds like you're entering the commands in command mode (aka. "Ex mode"). In that context :5d would remove line number 5, nothing else. For 5dd to work as intended -- that is, remove five consequent lines starting at the cursor -- enter it in normal mode and don't prefix the commands with :.

You can delete multiple(range) lines if you know the line numbers:

:[start_line_no],[end_line_no]d

Note: d stands for delete

where,
start_line_no is the beginning line no you want to delete and end_line_no is the ending line no you want to delete. The lines between the start and end, including start and end will be deleted.

Eg:

:45,101d

The lines between 45 and 101 including 45 and 101 will be deleted.