`grep -l .. | xargs vim` generates a warning, why?

Question

If I run a command like

grep -rl test . | xargs vim

I get a warning "Vim: Warning: Input is not from a terminal." But I am still able to edit the files. Why the warning?

Solution 1

Because Vim is invoked from inside the pipeline, the stdin is connected to the previous pipeline's output, not the terminal. As an interactive command, Vim needs to receive its input from the terminal.

Better avoid the pipe, e.g. via

$ vim $(grep -rl test .)

or from inside Vim:

:args `grep -rl test .`

Solution 2

Vim needs its standard input to be the terminal where you'll enter commands, but it gets either /dev/null or the pipe from grep depending on your xargs implementation.

You can restore standard input through an intermediate shell.

grep -rl test . | xargs sh -c 'vim -- "$@" <$0' /dev/tty

If the file names don't contain any whitespace character or any of \[?*, you can use command substitution instead:

vim $(grep -rl test .)

One way to cope with special characters (other than newline) is to restrict word splitting to newlines and turn off globbing.

(IFS='
'; set -f; exec vim $(grep -rl test .))

Solution 3

If you use GNU Parallel instead of xargs you do not get the warning and your terminal settings are not changed afterwards:

grep -rl test . | parallel -X --tty vi

Added bonus: It works even if filenames contain space, ' or ".

Comments

[lgeorget]

Related question: superuser.com/questions/336016/…

[kenorb]

Use: vim $(grep -rl test .) instead.

[kenorb]

Related: Terminal borked after invoking Vim with xargs at Vim SE

[lgeorget]

In this case, xargs' stdin is the pipeline, not vim's stdin.

[lgeorget]

vim's stdin is /dev/null if invoked with xargs.

[Stéphane Chazelas]

@lgeorget, that is not true of all xargs implementations. Solaris', and Busybox' at least don't (the spawned processes inherit the stdin of xargs, that is the pipe). That's not a POSIX requirement.

[lgeorget]

@StephaneChazelas Ok, it's worth knowing that. Thank you for the information!