Dockerfile capture output of a command
I have the following line in my Dockerfile which is supposed to capture the display number of the host:
RUN DISPLAY_NUMBER="$(echo $DISPLAY | cut -d. -f1 | cut -d: -f2)" && echo $DISPLAY_NUMBER
When I tried to build the Dockerfile, the DISPLAY_NUMBER is empty. But however when I run the same command directly in the terminal I get the see the result. Is there anything that I'm doing wrong here?
docker
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
add a comment |
I have the following line in my Dockerfile which is supposed to capture the display number of the host:
RUN DISPLAY_NUMBER="$(echo $DISPLAY | cut -d. -f1 | cut -d: -f2)" && echo $DISPLAY_NUMBER
When I tried to build the Dockerfile, the DISPLAY_NUMBER is empty. But however when I run the same command directly in the terminal I get the see the result. Is there anything that I'm doing wrong here?
docker
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
Is the$DISPLAYvariable empty when you rundocker build?
– Ricardo Branco
Nov 13 '18 at 19:34
Yes! The DISPLAY_NUMBER is empty!
– sparkr
Nov 13 '18 at 19:41
You can’t put that in a Dockerfile. What would happen if you ran the image from a different host, or (given your other questions) from a different ssh session with a different$DISPLAY?
– David Maze
Nov 13 '18 at 19:48
What do you want to achieve with this command?
– mbuechmann
Nov 13 '18 at 19:50
add a comment |
I have the following line in my Dockerfile which is supposed to capture the display number of the host:
RUN DISPLAY_NUMBER="$(echo $DISPLAY | cut -d. -f1 | cut -d: -f2)" && echo $DISPLAY_NUMBER
When I tried to build the Dockerfile, the DISPLAY_NUMBER is empty. But however when I run the same command directly in the terminal I get the see the result. Is there anything that I'm doing wrong here?
docker
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
I have the following line in my Dockerfile which is supposed to capture the display number of the host:
RUN DISPLAY_NUMBER="$(echo $DISPLAY | cut -d. -f1 | cut -d: -f2)" && echo $DISPLAY_NUMBER
When I tried to build the Dockerfile, the DISPLAY_NUMBER is empty. But however when I run the same command directly in the terminal I get the see the result. Is there anything that I'm doing wrong here?
docker
docker
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
asked Nov 13 '18 at 19:26
sparkrsparkr
5,0731243108
5,0731243108
Is the$DISPLAYvariable empty when you rundocker build?
– Ricardo Branco
Nov 13 '18 at 19:34
Yes! The DISPLAY_NUMBER is empty!
– sparkr
Nov 13 '18 at 19:41
You can’t put that in a Dockerfile. What would happen if you ran the image from a different host, or (given your other questions) from a different ssh session with a different$DISPLAY?
– David Maze
Nov 13 '18 at 19:48
What do you want to achieve with this command?
– mbuechmann
Nov 13 '18 at 19:50
add a comment |
Is the$DISPLAYvariable empty when you rundocker build?
– Ricardo Branco
Nov 13 '18 at 19:34
Yes! The DISPLAY_NUMBER is empty!
– sparkr
Nov 13 '18 at 19:41
You can’t put that in a Dockerfile. What would happen if you ran the image from a different host, or (given your other questions) from a different ssh session with a different$DISPLAY?
– David Maze
Nov 13 '18 at 19:48
What do you want to achieve with this command?
– mbuechmann
Nov 13 '18 at 19:50
Is the
$DISPLAY variable empty when you run docker build?– Ricardo Branco
Nov 13 '18 at 19:34
Is the
$DISPLAY variable empty when you run docker build?– Ricardo Branco
Nov 13 '18 at 19:34
Yes! The DISPLAY_NUMBER is empty!
– sparkr
Nov 13 '18 at 19:41
Yes! The DISPLAY_NUMBER is empty!
– sparkr
Nov 13 '18 at 19:41
You can’t put that in a Dockerfile. What would happen if you ran the image from a different host, or (given your other questions) from a different ssh session with a different
$DISPLAY?– David Maze
Nov 13 '18 at 19:48
You can’t put that in a Dockerfile. What would happen if you ran the image from a different host, or (given your other questions) from a different ssh session with a different
$DISPLAY?– David Maze
Nov 13 '18 at 19:48
What do you want to achieve with this command?
– mbuechmann
Nov 13 '18 at 19:50
What do you want to achieve with this command?
– mbuechmann
Nov 13 '18 at 19:50
add a comment |
2 Answers
2
active
oldest
votes
Host environment variables cannot be passed during build, only at run-time.
Only build args can be specified by:
first "declaring the arg"
ARG DISPLAY_NUMBER
and then running
docker build . --no-cache -t disp --build-arg DISPLAY_NUMBER=$DISPLAY_NUMBER
You can work around this issue using the envsubst trick
RUN echo $DISPLAY_NUMBER
And on the command line:
envsubst < Dockerfile | docker build . -f -
Which will rewrite the Dockerfile in memory and pass it to Docker with the environment variable changed.
Edit: Note that this solution is pretty useless though, because you probably
want to do this during run-time anyways, because this value should depend on not on where the image is built, but rather where it is run.
I would personally move that logic into your ENTRYPOINT or CMD script.
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
add a comment |
Commands specified with RUN are executed when the image is built. There is no display during build hence the output is empty.
You can exchange RUN with ENTRYPOINT then the command is executed when the docker starts.
But how to forward the hosts display to the container is another matter entirely.
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Host environment variables cannot be passed during build, only at run-time.
Only build args can be specified by:
first "declaring the arg"
ARG DISPLAY_NUMBER
and then running
docker build . --no-cache -t disp --build-arg DISPLAY_NUMBER=$DISPLAY_NUMBER
You can work around this issue using the envsubst trick
RUN echo $DISPLAY_NUMBER
And on the command line:
envsubst < Dockerfile | docker build . -f -
Which will rewrite the Dockerfile in memory and pass it to Docker with the environment variable changed.
Edit: Note that this solution is pretty useless though, because you probably
want to do this during run-time anyways, because this value should depend on not on where the image is built, but rather where it is run.
I would personally move that logic into your ENTRYPOINT or CMD script.
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
add a comment |
Host environment variables cannot be passed during build, only at run-time.
Only build args can be specified by:
first "declaring the arg"
ARG DISPLAY_NUMBER
and then running
docker build . --no-cache -t disp --build-arg DISPLAY_NUMBER=$DISPLAY_NUMBER
You can work around this issue using the envsubst trick
RUN echo $DISPLAY_NUMBER
And on the command line:
envsubst < Dockerfile | docker build . -f -
Which will rewrite the Dockerfile in memory and pass it to Docker with the environment variable changed.
Edit: Note that this solution is pretty useless though, because you probably
want to do this during run-time anyways, because this value should depend on not on where the image is built, but rather where it is run.
I would personally move that logic into your ENTRYPOINT or CMD script.
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
add a comment |
Host environment variables cannot be passed during build, only at run-time.
Only build args can be specified by:
first "declaring the arg"
ARG DISPLAY_NUMBER
and then running
docker build . --no-cache -t disp --build-arg DISPLAY_NUMBER=$DISPLAY_NUMBER
You can work around this issue using the envsubst trick
RUN echo $DISPLAY_NUMBER
And on the command line:
envsubst < Dockerfile | docker build . -f -
Which will rewrite the Dockerfile in memory and pass it to Docker with the environment variable changed.
Edit: Note that this solution is pretty useless though, because you probably
want to do this during run-time anyways, because this value should depend on not on where the image is built, but rather where it is run.
I would personally move that logic into your ENTRYPOINT or CMD script.
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
Host environment variables cannot be passed during build, only at run-time.
Only build args can be specified by:
first "declaring the arg"
ARG DISPLAY_NUMBER
and then running
docker build . --no-cache -t disp --build-arg DISPLAY_NUMBER=$DISPLAY_NUMBER
You can work around this issue using the envsubst trick
RUN echo $DISPLAY_NUMBER
And on the command line:
envsubst < Dockerfile | docker build . -f -
Which will rewrite the Dockerfile in memory and pass it to Docker with the environment variable changed.
Edit: Note that this solution is pretty useless though, because you probably
want to do this during run-time anyways, because this value should depend on not on where the image is built, but rather where it is run.
I would personally move that logic into your ENTRYPOINT or CMD script.
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
edited Nov 13 '18 at 19:59
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
answered Nov 13 '18 at 19:44
Uku LoskitUku Loskit
30.3k86879
30.3k86879
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
add a comment |
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
That will pass the display number of the machine where the image is built and print it out during build. I doubt that this makes any sense. If I wanted to know the display number of my current machine, I would just run the command there.
– mbuechmann
Nov 13 '18 at 19:49
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
I did not really consider the OP's intent, so in that sense your answer is probably more useful from a practical perspective. Although your answer has a small inaccuracy though, regarding as to why the variable is blank.
– Uku Loskit
Nov 13 '18 at 19:53
add a comment |
Commands specified with RUN are executed when the image is built. There is no display during build hence the output is empty.
You can exchange RUN with ENTRYPOINT then the command is executed when the docker starts.
But how to forward the hosts display to the container is another matter entirely.
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
add a comment |
Commands specified with RUN are executed when the image is built. There is no display during build hence the output is empty.
You can exchange RUN with ENTRYPOINT then the command is executed when the docker starts.
But how to forward the hosts display to the container is another matter entirely.
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
add a comment |
Commands specified with RUN are executed when the image is built. There is no display during build hence the output is empty.
You can exchange RUN with ENTRYPOINT then the command is executed when the docker starts.
But how to forward the hosts display to the container is another matter entirely.
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
Commands specified with RUN are executed when the image is built. There is no display during build hence the output is empty.
You can exchange RUN with ENTRYPOINT then the command is executed when the docker starts.
But how to forward the hosts display to the container is another matter entirely.
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
edited Nov 13 '18 at 19:44
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
answered Nov 13 '18 at 19:35
mbuechmannmbuechmann
2,82121325
2,82121325
add a comment |
add a comment |
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Is the
$DISPLAYvariable empty when you rundocker build?– Ricardo Branco
Nov 13 '18 at 19:34
Yes! The DISPLAY_NUMBER is empty!
– sparkr
Nov 13 '18 at 19:41
You can’t put that in a Dockerfile. What would happen if you ran the image from a different host, or (given your other questions) from a different ssh session with a different
$DISPLAY?– David Maze
Nov 13 '18 at 19:48
What do you want to achieve with this command?
– mbuechmann
Nov 13 '18 at 19:50