How to use an external command in Vim to modify selected words and lines?

Question

Something I've found useful in other editors is the ability to:

• take the selected text
• run an external command and pass the selection to its stdin
• take the external commands stdout and replace the current selection with it.

This way you can write useful text tools which operate on the selection using any language that can do basic io.

How can this be done with vim using the selection? ... a single character, word, paragraph... etc.

(Directly in the command line, or via a key binding?)

---

Note

Commands such as !sort work on the line-level, the reason I'm asking this question is because I would like to operate on the selection. (i.e., the text that would be removed if x was pressed).

Answer 1

I find that often the easiest way is to use visual mode with v (or capital V to select whole lines), and select the text you want to pipe.

Then type:

:!cat

This doesn't do anything useful, as such. A useful command I use often is:

:!python -m json.tool

to format JSON.

You can also just type (without visual mode):

:<range>!command

For example, for the entire file:

:%!python -m json.tool

Or for the current line:

:.!python -m json.tool

Answer 2

I wrote a plugin called express.vim that can help with this. The plugin defines an operator g= that lets you evaluate a VimScript expression over a motion (or Visual selection). It prompts for an expression, in which you can use v:val as a placeholder for the text covered by the motion (or, again, Visual selection).

In this case, a useful expression would use the system() function, which runs an external command.

system('tr a-z A-Z', v:val)

(Here I used tr as a simple example external command.)

The way to use express.vim for this problem would be to select the text with Visual mode, then type g= followed by that expression, then hit Enter:

g=system('tr a-z A-Z', v:val)<CR>

I'll admit, it's not easy to use. (In fact, I rarely use this plugin myself!) I'm considering adding a shortcut to invoke an external command, such as starting the expression with !. I'll post an update here if I end up doing that.

EDIT

I've modified express.vim to treat expressions beginning with ! as external commands. So, sticking with the tr example, the above becomes a lot simpler. After a Visual selection, type the following:

g=!tr a-z A-Z<CR>

Explanation:

1. Invoke the express operator with g=
2. Enter !tr a-z A-Z as the expression
3. Press Enter

Answer 3

You are looking for the filter commands in Vim. See :help filter. Here is the relevant documentation:

!{motion}{filter}   Filter {motion} text lines through the external
                    program {filter}.
!!{filter}          Filter [count] lines through the external program
                    {filter}.
{Visual}!{filter}   Filter the highlighted lines through the external
                    program {filter} (for {Visual} see |Visual-mode|).
                    {not in Vi}

:{range}![!]{filter} [!][arg]               *:range!*
                    Filter {range} lines through the external program
                   {filter}.  ...[See documentation for details]

So typing 5!!sort will sort the next 5 lines starting from the cursor.

Answer 4

Note that it can be done with:

1. visually select whatever you wish
2. s^R=system('tr a-z A-Z', @")[:-2]^M (with ^R being CTRL+R, and ^M being ENTER)

It could also work with anything that does selection + replace like ci"^R=....

Answer 5

There is a vim plugin called vis.vim which allows this functionality. I found it on this stack overflow post: https://stackoverflow.com/questions/40072761/vim-send-visual-block-to-external-command#answer-40083050