How to run an external filter on a part of a line?

Question

How do I run an external filtering program on a part of a line?

When I do:

:'<,'>!myfilter

it always filters the whole line regardless of whether the whole line is selected or just a part of it.

you can't since ex commands are by default linewise. Easiest way is to copy the line and remove the parts that you do not want to filter. Alternatively, using a plugin like my NarrowRegion plugin may help. — Christian Brabandt, Commented Apr 29, 2020 at 12:27
As Christian says, :! and other ex commands work line-by-line, so it filters the whole lone. You cant change this behavior, but you can do workarounds... a good answer will demonstrate such workarounds. — D. Ben Knoble, Commented Apr 29, 2020 at 13:01

user938271 · Accepted Answer · 2020-04-29 13:41:32Z

Try this:

 :s/\%V.*\%V./\=system('myfilter', submatch(0))[:-2]/

As an example, consider this text:

one  zwei three
four fünf six

Visually select the block containing the german numbers zwei and fünf, and run this command:

:'<,'>s/\%V.*\%V./\=system('trans -brief', submatch(0))[:-2]/

It should translate the numbers into english:

one  two three
four five six

Requires the shell utility translate-shell.

To make the process a little easier, you could install this mapping:

xno <c-g>s :s/\%V.*\%V./\=system('', submatch(0))[:-2]/<c-r>=setcmdpos(28)[-1]<cr>

Press C-g s while selecting your text. It should populate the command-line with:

:'<,'>s/\%V.*\%V./\=system('', submatch(0))[:-2]/
                            ^
                            cursor right before

And the cursor should be correctly positioned to let you immediately type the name of the filter you want to use.

For more info, see:

:h /\%V
:h system()
:h submatch()
:h setcmdpos()

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