Replace last instance of character (and there's more)

Question

I am trying to format a list that uses tabs for indentation so it will render as a bulleted list on Confluence. That means that each instance of a tab needs to be replaced with an asterisk (*), plus one leading asterisk, and then a space at the end of the string of asterisks.

Example:

Level 1
\tLevel 2
\tLevel 2
\t\tLevel 3
\tLevel 2
Level 1

Would become:

* Level 1
** Level 2
** Level 2
*** Level 3
** Level 2
* Level 1

I have tried doing a global replace (s/\t/\*/g) and then adding an asterisk at the beginning of each line, but that leaves me without the trailing space. I also tried the \ze atom as detailed here (s/\*\ze/\* /), but that replaces the first asterisk, not the last. I feel like I'm really close but there's something I'm missing that will make this clear.

Answer 1

Here's a solution I came up with:

:%s/^\(\t*\)/\="*" . substitute(submatch(1), '\t', '\*', 'g') . " "/

• %s///: Do a substitute on every line in the file
• ^\(\t*\): Match as many tabs as you can find at the beginning of the line
• \=: Allows us to use an expression in the replacement
• substitute(submatch(1), '\t', '\*', 'g'): Replace all the tabs with asterisks. (The submatch(1) selects the the first group of "memory parentheses" \(\))
• "*" . ... . " ": Prepend an asterisk and append a space character

See :h submatch and :h sub-replace-\= for more info.

Answer 2

I imagine the easiest way is to run 2 simple substitutions.

:%s/\t/*/g
:%s/\w/* &/

The first to replaces tab characters with stars and the second to puts an additional star and space before the first character.

If you can't use the % range then you can combine this with the global command, :g, to execute a command on each line that matches a pattern.

:g/^\t*/s/\t/*/g|s/\w/* &

We use the | to run 2 separate commands so we can run multiple commands in one line.

For more help see:

:h :s
:h s/\\&
:h /\w
:h :g
:h :|