How can I run :substitute on only part of the line and not all of it?

Question

I have a line like this one:

function my_function(argument, another argument, but there are spaces)

I want to substitute the space characters (inside the argument's names) with underscore. I thus would like to use :

:s/\ /_/g

but how can I choose not to apply it to the whole line, but starting from, say, the cursor position ? (Or the third word) ?

Answer 1

You could use the following solution:

First use v$ to select the text from the cursor to the end of the line. Then use the following command:

:s/\%V\ /_/g

The \%V indicate to change the text in the previously visually selected area, see :h /\%V.

If I take your example:

function my_function(argument, another argument, but there are spaces)

If my cursor is on the 40th column and I use the command I just wrote I get:

function my_function(argument, another argument,_but_there_are_spaces)

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In answer to your comment you can also use

• \%# which matches from the cursor position
• \%>23c which matches after the 23rd column.
• \%>'m which matches after the position of a mark

See :h /\%#, :h /\%>c and :h /\%>'m.

@User9433424 gave a way to use \%# in his comment. For the pattern with the mark you can set it wit ma and then use:

:s/\%>'a /_/g

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An explanation of the pattern given by @User9433424 is the following:

:s/\v(%#.*)@<= /_/
:s/                    substitution command
   \v                  Enable the very magic mode
      %#.*             Any characters from the cursor position
           @<=         Check for matches just before what follows
              space    Followed by a space
               /_/     Substitute the matches by underscores

You'll want to see :h \v and :h /\@<=

Answer 2

You can use look behind (:h \@<=) to make sure there is a preceding '(', and an end-of-word boundary (:h \>) to make sure the substitution happens where you want it.

So, with the text:

function my_function(argument, another argument, but there are spaces)

running the command:

:s/\((.*\)\@<=\> /_/g

will produce:

function my_function(argument, another_argument, but_there_are_spaces)

This might be easier than having to position the cursor each time, provided the substitution always has a known starting point.