[Vim handling stdin]

Tags: #vim #stdin

Vim handling stdin.md

Note: for full details, read https://vimways.org/2018/vims-social-life/

Vim doesn’t handle stdin like other posix commands…

$ echo foo | vim

Vim: Warning: Input is not from a terminal
Vim: Error reading input, exiting...
Vim: Finished.

If you pass - to vim, then it will accept the stdin and copy it to a new buffer…

$ echo foo | vim -

Before we look ahead at how to handle stdin a bit better, let’s consider the + flag which tells vim what line to start on (the following example tells vim to jump to line 10):

$ vim ~/.vimrc +10

This will become relevant when we look at two other flags -e and -s (see vim -h for more information on available flags)…

$ echo foo | vim - -es +'%p' +'qa!'

Vim: Reading from stdin...
foo

When using the -e and -s flags, we’re able to use + to execute Ex mode commands (see :help -s-ex).

Note: if you don’t use +'qa!' then vim will cause the terminal to hang (you also need the ! otherwise qa would – if dealing with a traditional vim UI – show a message saying the buffer has been edited and can’t be quite).

To avoid the Vim: Reading from stdin... message we need an additional flag --not-a-term:

$ echo foo | vim - -es +'%p' +'qa!' --not-a-term

foo

So now if we want to manipulate the content (let’s say uppercase the word foo to FOO) we can do:

$ echo foo | vim - -es --not-a-term +'norm VgU' +'%p' +'qa!'

FOO

Note: norm says execute the following characters as if the user is typing them, so V selects the entire line and gU uppercases the selection. We then print the output to stdout %p and then quit without trying to save the modifications.