scp/rsync autocomplete can hang if command-not-found enabled

[Jonathan]

Referencing my post at http://superuser.com/a/1026307/156478

AlexO'Neill wrote:

>Here is my scenario:
>
>I want to transfer ~/foo.txt to a server aoneill@bar.
>
>I start typing in my command line:
>
>aoneill@aoneill-Laptop:~$ scp fo
>
>At this point I hit <tab> to complete the file name, and my terminal just freezes up. It won't change based on any keystroke, and the cursor is just stuck right next to the fo, unless I <ctrl-C> out.
>

Using set -x shows that the autocomplete was hanging on ruptime.

 $ set -x
 $ scp fo local cur prev words cword
+ _init_completion -n :
...
+ COMPREPLY+=($( compgen -W "$( ruptime 2>/dev/null | awk '!/^ruptime:/ { print $1 }' )" -- "$cur" ))
+++ ruptime
+++ awk '!/^ruptime:/ { print $1 }'

When I tried to run ruptime myself I found that it wasn't installed. After installing the rwho package the hang was fixed.

sudo apt-get install rwho

The COMPREPLY line calls ruptime without checking to see if it exists. And since I have 'COMMAND_NOT_FOUND_INSTALL_PROMPT=1' enabled the command tries to ask me if I want to install it but the pipe captures the output and hangs.

So the bug happens because command-not-found doesn't check if its being used in a pipe.

The simplest reproduction of this bug was running the following command "wdf 2>/dev/null | grep asdf" assuming wdf isn't installed and is a valid command.

I've attached an example patch that checks whether the command is attached to a real terminal before continuing.