How to run command during Docker build which requires a tty?

Question

I have some script I need to run during a Docker build which requires a tty (which Docker does not provide during a build). Under the hood the script uses the read

Answer 1

RUN <command> in Dockerfile reference:

shell form, the command is run in a shell, which by default is /bin/sh -c on Linux or cmd /S /C on Windows

let's see what exactly /bin/sh is in ubuntu:14.04:

$ docker run -it --rm ubuntu:14.04 bash
root@7bdcaf403396:/# ls -n /bin/sh
lrwxrwxrwx 1 0 0 4 Feb 19  2014 /bin/sh -> dash

/bin/sh is a symbolic link of dash, see read function in dash:

$ man dash
...
read [-p prompt] [-r] variable [...]
            The prompt is printed if the -p option is specified and the standard input is a terminal.  Then a line
            is read from the standard input.  The trailing newline is deleted from the line and the line is split as
            described in the section on word splitting above, and the pieces are assigned to the variables in order.
            At least one variable must be specified.  If there are more pieces than variables, the remaining pieces
            (along with the characters in IFS that separated them) are assigned to the last variable.  If there are
            more variables than pieces, the remaining variables are assigned the null string.  The read builtin will
            indicate success unless EOF is encountered on input, in which case failure is returned.

            By default, unless the -r option is specified, the backslash ``\'' acts as an escape character, causing
            the following character to be treated literally.  If a backslash is followed by a newline, the backslash
            and the newline will be deleted.
...

read function in dash:

At least one variable must be specified.

let's see read function in bash:

$ man bash
...
read  [-ers]  [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name...]
If  no names are supplied, the line read is assigned to the variable REPLY.  The return code is zero,
              unless end-of-file is encountered, read times out (in which case the  return  code  is  greater  than
              128), or an invalid file descriptor is supplied as the argument to -u.
...

So I guess your script myscript.sh is start with #!/bin/bash or something else but not /bin/sh.

Also, you can change your Dockerfile like below:

FROM ubuntu:14.04
RUN echo yes | read ENV_NAME

Links:

• https://docs.docker.com/engine/reference/builder/
• http://linux.die.net/man/1/dash
• http://linux.die.net/man/1/bash

Answer 2

You don't need a tty for feeding your data to your script . just doing something like (echo yes; echo no) | myscript.sh as you suggested will do. also please make sure you copy your file first before trying to execute it . something like COPY myscript.sh myscript.sh

Answer 3

Most likely you don't need a tty. As the comment on the question shows, even the example provided is a situation where the read command was not properly called. A tty would turn the build into an interactive terminal process, which doesn't translate well to automated builds that may be run from tools without terminals.

If you need a tty, then there's the C library call to openpty that you would use when forking a process that includes a pseudo tty. You may be able to solve your problem with a tool like expect, but it's been so long that I don't remember if it creates a ptty or not. Alternatively, if your application can't be built automatically, you can manually perform the steps in a running container, and then docker commit the resulting container to make an image.

I'd recommend against any of those and to work out the procedure to build your application and install it in a non-interactive fashion. Depending on the application, it may be easier to modify the installer itself.