Can you pass specific text within a line to an external command?

Question

Background

Vim uses ranges to specify which lines should be passed to a command. For example, :5,10 will use lines 5-10, :'a,'b will use the lines between mark a and mark b, and :'<,'> will use the lines that are selected in visual mode.

Question

Is there a way to do this with sub-line granularity? What if I want to use only part of a line instead of the whole line?

Example use case

I want to pass some text within my file into an external shell program. For example, I can use write_c (see :help w_c) to pass some text into cat, which will just print it out. Let's say I have the following file:

hello
this is my file
goodbye

and I put my cursor on the m. Then I use v to enter visual mode and fe to go to the next e. Now my visual selection is my file. If I then press : to enter command mode and type :w !cat (so the entire command is :'<,'>:w !cat), then I see the message this is my file, when I only wanted to see my file because the entire line that the visual selection was on got piped into cat.

How can I select just my file and pipe only that part into cat?

Answer 1

Short answer

You can't. Ex commands are always linewise and there is no way around that.

Long answer

You can achieve your goal, though, just not with :help :range! or any other Ex command.

You can start with a relatively straightforward method (that happens to fit your simple example):

vfe
y
:w !cat <C-r>"<CR> 

but it quickly becomes rather complex when you start to deal with multiline text, special characters, etc.. And then, you have to consider what the external command expects: does it need \n-terminated line? does it handle multiline? what about quoting and expansion? etc.

Here is the same example, but with some sanitization added:

:w !cat <C-r>=shellescape(getreg('"'))<CR>

This is starting to become a lot more involved than:

:'<,'>w !cat

and we are not doing anything even remotely useful with that text.

See :help system() for another even more involved approach.

Answer 2

Thanks to @romainl for the help. Here's a solution that uses yanking and seems to work well:

1. y to yank the selection
2. :!echo to start the command
3. <C-r>=escape(substitute(shellescape(getreg('"')), '\n', '\r', 'g'), '#%!')<CR> to put the contents of the " register into the command line
4. <Bar> cat to pipe the result into cat (for example)
5. <CR><CR> to run the command

An example overall mapping looks like this:

vnoremap <C-c> y:!echo <C-r>=escape(substitute(shellescape(getreg('"')), '\n', '\r', 'g'), '#%!')<CR> <Bar> clip.exe<CR><CR>

Using this, I can map Ctrlc in visual mode to copy text to the clipboard using clip.exe in WSL.

So far this works for all the visual highlight cases I have tested:

• normal text
• multiline text
• text including ', ", (, ), #, %, or !
• visual block selections
• text ending in a newline (including visual line mode selections)

So I'm happy with it for now. Hopefully there isn't some weird case I come across later that breaks it...