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
command. With a tty, I can do things like (echo yes; echo no) | myscript.sh
.
Without it I get strange errors I don't completely understand. So is there any way to use this script during the build (given that its not mine to modify?)
EDIT: Here's a more definite example of the error:
FROM ubuntu:14.04
RUN echo yes | read
which fails with:
Step 0 : FROM ubuntu:14.04
---> 826544226fdc
Step 1 : RUN echo yes | read
---> Running in 4d49fd03b38b
/bin/sh: 1: read: arg count
The command '/bin/sh -c echo yes | read' returned a non-zero code: 2
The -t (or --tty) flag tells Docker to allocate a virtual terminal session within the container. This is commonly used with the -i (or --interactive) option, which keeps STDIN open even if running in detached mode (more about that later).
If you need to run a command inside a running Docker container, but don't need any interactivity, use the docker exec command without any flags: docker exec container-name tail /var/log/date.
You can now drop into your Docker image and start interactively running commands! You can keep running these steps, commenting out your Dockerfile, dropping into a shell, and figuring out problematic commands, until your Docker images builds perfectly.
The docker exec command runs a new command in a running container. The command started using docker exec only runs while the container's primary process ( PID 1 ) is running, and it is not restarted if the container is restarted. COMMAND will run in the default directory of the container.
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:
Short answer : You can't do it straightly because docker build
or either buildx
didn't implement [/dev/tty
, /dev/console
]. But there is a hacky solution where you can achieve what you need but I highly discourage using it since it break the concept of CI. That's why docker didn't implement it.
Hacky solution
FROM ubuntu:14.04
RUN echo yes | read #tty requirement command
As mentioned in docker reference document the RUN
consist of two stage, first is execution of command and the second is commit to the image as a new layer. So you can do the stages manually on your own where we will provide tty to first stage(execution) and then commit the result.
Code:
cd
cat >> tty_wrapper.sh << EOF
echo yes | read ## Your command which needs tty
rm /home/tty_wrapper.sh
EOF
docker run --interactive --tty --detach --privileged --name name1 ubuntu:14.04
docker cp tty_wrapper.sh name1:/home/
docker exec name1 bash -c "cd /home && chmod +x tty_wrapper.sh && ./tty_wrapper.sh "
docker commit name1 your:tag
Your new image is ready. Here is a description about the code. At first we make a bash script which wrap our tty to it and then remove itself after fist execute. Then we run a container with provided tty option(you can remove privileged if you don't need). Next step we copy wrapped bash script inside container and do the execution & commit stage on our own.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With