fin exec no-tty mode

[lmakarov]

Output from fin exec cannot be used for string comparison directly.
This is due to docker exec spitting out \r\n line ending even on Mac. Additionally, on Windows a special hidden flag should be set for winpty to enable dumb terminal mode.

On Mac apply tr -d '[:cntrl:]'
On Windows apply winpty -Xplain and tr -d '[:cntrl:]'

[lmakarov]

Apparently the the \r\n sequence is only present when tty (-t) is used with docker run/exec

$ docker run --rm busybox pwd | od -c
0000000    /  \n                                                        
0000002

$ docker run --rm -t busybox pwd | od -c
0000000    /  \r  \n                                                    
0000003

The corresponding docker issue moby/moby#8513 (comment)

Moral of the story, don't use -t unless you want a TTY.
TTY line endings are CRLF, this is not Docker's doing.

We will still have to handle the case with Windows and winpty in fin exec.

[lmakarov]

On Windows

$ docker run --rm busybox pwd | od -c
0000000   /  \n
0000002
$ docker run --rm -i busybox pwd | od -c
0000000   /  \n
0000002
$ docker run --rm -t busybox pwd | od -c
0000000   /  \r  \n
0000003
$ docker run --rm -it busybox pwd | od -c
the input device is not a TTY.  If you are using mintty, try prefixing the command with 'winpty'
0000000

Now if we add winpty to the mix

$ winpty -Xallow-non-tty -Xplain docker run --rm busybox pwd | od -c
0000000   /  \r  \n
0000003
$ winpty -Xallow-non-tty -Xplain docker run --rm -i busybox pwd | od -c
0000000   /  \r  \n
0000003
$ winpty -Xallow-non-tty -Xplain docker run --rm -t busybox pwd | od -c
0000000   /  \r  \n
0000003
$ winpty -Xallow-non-tty -Xplain docker run --rm -it busybox pwd | od -c
0000000   /  \r  \n
0000003

Proposed flag for fin exec (similar to what docker-compose is doing):

    -T                Disable pseudo-tty allocation. By default `docker-compose exec`
                      allocates a TTY.

When set, -t on docker exec will not be set and winpty will not be used (on Windows).