Setting variables with executing a command with exec - bash

You can set a variable for a single command like this:
MY_VARIABLE=my_value ./my_script.sh
You can hand off to another script like this:
exec ./my_script.sh
But when I try to do both like this:
exec MY_VARIABLE=my_value ./my_script.sh
I get an error:
exec: MY_VARIABLE=my_value: not found
Why is that?
Is there any way to do this?

You need to use env to specify the environment variable:
exec env MY_VARIABLE=my_value ./my_script.sh
If you want your script to start with an empty environment or with only the specified variables, use the -i option.
From man env:
env - run a program in a modified environment

In bash, you can set environment variables for a command by putting the assignments at the beginning of the command. This works the same for exec as any other command, so you write:
MYVARIABLE=my_value exec ./my_script.sh

Related

Why exporting env var in bash script does not affect env?

I want to set env variable in shell script. Shell script content is:
#!/bin/bash
export XDEBUG_CONFIG="idekey=PHPSTORM"
I tried both bash bin/enable_debug and bin/enable_debug. After both command I get:
$ echo $XDEBUG_CONFIG
$
However if I run export XDEBUG_CONFIG="idekey=PHPSTORM" directly in cli it works. What's wrong with my method?
You can try running your script as below:
. bin/enable_debug
OR
source bin/enable_debug
as indicated by #Aserre

Why Can't I Set Env Variables By Running A BASH Script From An Npm Script?

I have a nodejs javascript project, but I would like to set a bunch of environment variables locally. created a bash file that just exports some variables:
#!/usr/bin/env bash
export waka=flaka
export fat=booty
When I use the dot to source and run the file from the command line it works fine:
. ./env.sh
And I can see the variable has been set
echo $waka # prints "flaka"
But then I try to take this command and make it an npm script by adding it to my package.json
scripts: {
"set-env": ". ./env.sh",
...
}
and then run it:
npm run set-env
The script is run but the environment variables are not saved:
echo $waka # prints undefined (assuming you didn't already run it from command line)
So, I'm wondering why it doesn't save the envrionment variables as an npm script and if it's possible to run the bash script from an npm script in a way such that the environment variables will be saved for the rest of the command prompt session. Thanks!
npm is not a shell command; it runs in a separate process that forks another shell in order to run the command specified by set-env. env.sh is executed, but then that shell immediately exits, at which point the changes are gone (and then npm itself exits).

Dockerfile assign bash command to var

I need to assign bash command to var in Dockerfile. Following is what I guess:
FROM centos:7
RUN data=$(ls /)
ENV DATA $data
After running container (docker run exec -it <image> bash), then echo $DATA output is empty. I have searched on google, but noway. I am stuck!
How to assign bash command to value in dockerfile?
You can't do that, since RUN command spawns its own shell.
Alternatively, you can save the information to some file, and use an ENTRYPOINT to set the env variable using some script once the container is running.
You can't set any variables while building docker image, because image build as layered filesystem, after executing RUN command instruction, it will execute command in run time and exit, so you can write docker file like below:
FROM centos:7
RUN echo 'export data=$(ls /)' >> ~/.bashrc
ENV DATA $data

Unable to pass variables to run docker container [duplicate]

If I set an environment variable, say ENV ADDRESSEE=world, and I want to use it in the entry point script concatenated into a fixed string like:
ENTRYPOINT ["./greeting", "--message", "Hello, world!"]
with world being the value of the environment varible, how do I do it? I tried using "Hello, $ADDRESSEE" but that doesn't seem to work, as it takes the $ADDRESSEE literally.
You're using the exec form of ENTRYPOINT. Unlike the shell form, the exec form does not invoke a command shell. This means that normal shell processing does not happen. For example, ENTRYPOINT [ "echo", "$HOME" ] will not do variable substitution on $HOME. If you want shell processing then either use the shell form or execute a shell directly, for example: ENTRYPOINT [ "sh", "-c", "echo $HOME" ].
When using the exec form and executing a shell directly, as in the case for the shell form, it is the shell that is doing the environment variable expansion, not docker.(from Dockerfile reference)
In your case, I would use shell form
ENTRYPOINT ./greeting --message "Hello, $ADDRESSEE\!"
After much pain, and great assistance from #vitr et al above, i decided to try
standard bash substitution
shell form of ENTRYPOINT (great tip from above)
and that worked.
ENV LISTEN_PORT=""
ENTRYPOINT java -cp "app:app/lib/*" hello.Application --server.port=${LISTEN_PORT:-80}
e.g.
docker run --rm -p 8080:8080 -d --env LISTEN_PORT=8080 my-image
and
docker run --rm -p 8080:80 -d my-image
both set the port correctly in my container
Refs
see https://www.cyberciti.biz/tips/bash-shell-parameter-substitution-2.html
I tried to resolve with the suggested answer and still ran into some issues...
This was a solution to my problem:
ARG APP_EXE="AppName.exe"
ENV _EXE=${APP_EXE}
# Build a shell script because the ENTRYPOINT command doesn't like using ENV
RUN echo "#!/bin/bash \n mono ${_EXE}" > ./entrypoint.sh
RUN chmod +x ./entrypoint.sh
# Run the generated shell script.
ENTRYPOINT ["./entrypoint.sh"]
Specifically targeting your problem:
RUN echo "#!/bin/bash \n ./greeting --message ${ADDRESSEE}" > ./entrypoint.sh
RUN chmod +x ./entrypoint.sh
ENTRYPOINT ["./entrypoint.sh"]
I SOLVED THIS VERY SIMPLY!
IMPORTANT: The variable which you wish to use in the ENTRYPOINT MUST be ENV type (and not ARG type).
EXAMPLE #1:
ARG APP_NAME=app.jar # $APP_NAME can be ARG or ENV type.
ENV APP_PATH=app-directory/$APP_NAME # $APP_PATH must be ENV type.
ENTRYPOINT java -jar $APP_PATH
This will result with executing:
java -jar app-directory/app.jar
EXAMPLE #2 (YOUR QUESTION):
ARG ADDRESSEE="world" # $ADDRESSEE can be ARG or ENV type.
ENV MESSAGE="Hello, $ADDRESSEE!" # $MESSAGE must be ENV type.
ENTRYPOINT ./greeting --message $MESSAGE
This will result with executing:
./greeting --message Hello, world!
Please verify to be sure, whether you need quotation-marks "" when assigning string variables.
MY TIP: Use ENV instead of ARG whenever possible to avoid confusion on your part or the SHELL side.
For me, I wanted to store the name of the script in a variable and still use the exec form.
Note: Make sure, the variable you are trying to use is declared an environment variable either from the commandline or via the ENV directive.
Initially I did something like:
ENTRYPOINT [ "${BASE_FOLDER}/scripts/entrypoint.sh" ]
But obviously this didn't work because we are using the shell form and the first program listed needs to be an executable on the PATH. So to fix this, this is what I ended up doing:
ENTRYPOINT [ "/bin/bash", "-c", "exec ${BASE_FOLDER}/scripts/entrypoint.sh \"${#}\"", "--" ]
Note the double quotes are required
What this does is to allow us to take whatever extra args were passed to /bin/bash, and supply those same arguments to our script after the name has been resolved by bash.
man 7 bash
-- A -- signals the end of options and disables further
option processing. Any arguments after the -- are treated
as filenames and arguments. An argument of - is
equivalent to --.
In my case worked this way: (for Spring boot app in docker)
ENTRYPOINT java -DidMachine=${IDMACHINE} -jar my-app-name
and passing the params on docker run
docker run --env IDMACHINE=Idmachine -p 8383:8383 my-app-name
I solved the problem using a variation on "create a custom script" approach above. Like this:
FROM hairyhenderson/figlet
ENV GREETING="Hello"
RUN printf '#!/bin/sh\nfiglet -W \${GREETING} \$#\n' > /runme && chmod +x /runme
ENTRYPOINT ["/runme"]
CMD ["World"]
Run like
docker container run -it --rm -e GREETING="G'Day" dockerfornovices/figlet-greeter Alec
If someone wants to pass an ARG or ENV variable to exec form of ENTRYPOINT then a temp file created during image building process might be used.
In my case I had to start the app differently depending on whether the .NET app has been published as self-contained or not.
What I did is I created the temp file and I used its name in the if statement of my bash script.
Part of my dockerfile:
ARG SELF_CONTAINED=true #ENV SELF_CONTAINED=true also works
# File has to be used as a variable as it's impossible to pass variable do ENTRYPOINT using Exec form. File name allows to check whether app is self-contained
RUN touch ${SELF_CONTAINED}.txt
COPY run-dotnet-app.sh .
ENTRYPOINT ["./run-dotnet-app.sh", "MyApp" ]
run-dotnet-app.sh:
#!/bin/sh
FILENAME=$1
if [ -f "true.txt" ]; then
./"${FILENAME}"
else
dotnet "${FILENAME}".dll
fi
Here is what worked for me:
ENTRYPOINT [ "/bin/bash", "-c", "source ~/.bashrc && ./entrypoint.sh ${#}", "--" ]
Now you can supply whatever arguments to the docker run command and still read all environment variables.

How to Set docker container ip to environment variable dynamically on startup?

I want to export docker container hostname as an environment variable which I can later use in my app. In my docker file I call my script "run" as last command
CMD run
The run file is executable and works fine with rest of commands I perform but before them I want to export container hostname to an env. variable as follows
"run" File Try 1
#!/bin/bash
export DOCKER_MACHINE_IP=`hostname -i`
my_other_commands
exec tail -f /dev/null
But when I enter docker container and check, the variable is not set. If I use
echo $DOCKER_MACHINE_IP
in run file after exporting, it shows ip on console when I try
docker logs
I also tried sourcing another script from "run" file as follows
"run" File Try 2
#!/bin/bash
source ./bin/script
my_other_commands
exec tail -f /dev/null
and the script again contains the export command. But this also does not set the environment variable. What I am doing wrong?
When you execute a script, any environment variable set by that script will be lost when the script exits.
But for both the cases you've posted above the environment variable should be accessible for the commands in your scripts, but when you enter the docker container via docker run you will get a new shell, which does not contain your variable.
tl;dr Your exported environment variable will only be available to sub shells of the shell which set the variable. And if you need it when logging in you should source the ./bin/script file.

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