How to write whole buffer to standard output from the command line?

Question

I would like to write whole buffer into standard output (/dev/stdout) instead of the file and the following command works as expected while editing the file:

:w >> /dev/stdout

^{Hint: Press Control+L to refresh the screen.}

But it doesn't work as expected when I'm trying to do the same from the command line (non-interactively), in example:

$ echo This is example. | vim - '+:w >> /dev/stdout' '+:q!'
Vim: Reading from stdin...

The same with :w !tee, :x! /dev/stdout, :%print and similar.

Before quit, it's saying: [Device] 1L, 17C appended.

Is there any way of forcing vim to write the standard input into standard output in the middle of a pipe? Maybe it's somehow buffered?

Answer 1

To print buffer to shell standard output, vim needs to start in Ex mode, otherwise it'll open "normal" way with its own window and clear any output buffers on quit.

Here is the simplest working example:

$ echo foo | vim -e '+%print' '+q!' /dev/stdin
foo

or even shorter:

$ echo foo | ex +%p -cq! /dev/stdin
$ echo foo | ex +"%p|q!" /dev/stdin

^{Note: The command vim -e is basically equivalent to ex command.}

Special file descriptor to standard input needs to be specified (/dev/stdin) in order to prevent extra annoying messages (as explained below).

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And here are some examples with parsing strings:

$ echo This is example. | vim -e '+s/example/test/g' '+%print' '+q!' /dev/stdin
This is test.
$ echo This is example. | vim - -es '+s/example/test/g' '+%print' '+q!'
Vim: Reading from stdin...
This is test.

^{Note: The last example shows extra annoying message which is not possible to hide it, it's because a standard strategy of reading the whole file into memory and saying it was read from the standard input. The first example works without the message, because the file produce endless data without an end-of-file (EOF) signal, so it'll will never reach the end of its input reading.}

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Related:

• How to write buffer content to stdout? at stackoverflow
• Pipe Vim buffer to stdout at stackoverflow

Answer 2

vipe is a convenient tool for editing pipelines, part of the moreutils package. It is a wrapper for editors (including the vi which gives it its name). It uses the EDITOR environment variable to set the editor, so, like with other tools that make use of EDITOR (such as crontab, visudo, etc.), you can script actions using that variable. For example, you can change it to do:

$ echo foo | EDITOR='vim +:s/foo/bar/ +wq' vipe | tail
bar

Of course, complicated actions might devolve to quoting hell, so you could write a script:

#! /bin/sh

vim "+:s/foo/bar" '+wq' "$@"

And use EDITOR="sh /path/to/script".