I want to write a line of text to a textfile INSIDE a running docker container. Here's what I've tried so far:
docker exec -d app_$i eval echo "server.url=$server_url" >> /home/app/.app/app.config
Response:
/home/user/.app/app.config: No such file or directory
Second try:
cfg_add="echo 'server.url=$server_url' >> /home/user/.app/app.config"
docker exec -i app_$i eval $cfg_add
Response:
exec: "eval": executable file not found in $PATH
Any ideas?
eval is a shell builtin, whereas docker exec requires an external utility to be called, so using eval is not an option.
Instead, invoke a shell executable in the container (bash) explicitly, and pass it the command to execute as a string, via its -c option:
docker exec "app_$i" bash -c "echo 'server.url=$server_url' >> /home/app/.app/app.config"
By using a double-quoted string to pass to bash -c, you ensure that the current shell performs string interpolation first, whereas the container's bash instance then sees the expanded result as a literal, as part of the embedded single-quoted string.
As for your symptoms:
/home/user/.app/app.config: No such file or directory was reported, because the redirection you intended to happen in the container actually happened in your host's shell - and because dir. /home/user/.app apparently doesn't exist in your host's filesystem, the command failed fundamentally, before your host's shell even attempted to execute the command (bash will abort command execution if an output redirection cannot be performed).
Thus, even though your first command also contained eval, its use didn't surface as a problem until your second command, which actually did get executed.
exec: "eval": executable file not found in $PATH happened, because, as stated, eval is not an external utility, but a shell builtin, and docker exec can only execute external utilities.
Additionally:
If you need to write text from outside the container, this also works:
(docker exec -i container sh -c "cat > c.sql") < c.sql
This will pipe you input into the container. Of course, this would also work for plain text (no file). It is important to leave off the -t parameter.
See https://github.com/docker/docker/pull/9537
UPDATE (in case you just need to copy files, not parts of files):
Docker v17.03 has docker cp which copies between the local fs and the container: https://docs.docker.com/engine/reference/commandline/cp/#usage
try to use heredoc:
(docker exec -i container sh -c "cat > /test/iplist") << EOF
10.99.154.146
10.99.189.247
10.99.189.250
EOF
Related
I have a bash script running inside a docker container. In this script, I set the value of some variable.
Can I somehow access the value of this variable outside the container?
I tried to make the variable "global" but could not figure out how to do it. Is it a good idea to make the required variable an environment variable inside the container?
How to reproduce
Create a bash script called temp.sh with the following contents:
a=$RANDOM
Now, run this file in a docker container as follows:
docker run -it --rm -v $(pwd):/opt alpine sh -c "sh /opt/temp.sh"
Desired behaviour: To be able to access the variable a outside the docker container
Credit: This comment by Mark
I mounted a directory on the docker filesystem using
docker run -v <host-file-system-directory>:<docker-file-system-directory>
In the bash script, I added
echo "$variable" >docker-file-system-directory/variable.txt
As I had mounted a host filesystem directory on the docker filesystem, I can still access variable.txt simply using cat <host-file-system-directory>/variable.txt
Note that docker-file-system-directory must be an absolute path, and not a relative path.
One way of achieving that is using docker exec, if your container is running and has access to bash.
#!/usr/bin/env bash
set -x
yourContainerName="testContainerName"
test=$(docker exec -i "${yourContainerName}" bash <<EOF
# do some work here e.g. execute your script
testVar="thisIsTest" # the value we want to access outside of container
echo \$testVar
EOF
)
echo $test
We pass a multiline script to docker container, which in the end echo's the value we need. This value is then accessible from shell that executed docker exec.
Output looks like this:
++ docker exec -i testContainerName bash
+ test=thisIsTest
+ echo thisIsTest
thisIsTest
I try to run docker run from bash script and docker says:
“is not a docker command”
If I print the docker command line before I called docker and I copy it to clipboard and paste it to command line it works well!
here is the command in bash script:
local args="run ${nw_param} ${opts} --name ${img} ${repository}/${img}:${tag}"
docker ${args}
the current echo of args string is:
run --net=ehvb-network -d --restart=always --name my-module my-private-registry:5000/my-module:0.0.1-1555334810
When I copied this string to the clipboard and paste it to command line it works well.
I use Debian stretch. My script is using bash (#!/bin/bash)
When I remove ${opts} it runs from bash. Opts currently contains “-d --restart=always”. When I try to use only -d or only --restart=always it works well. But when I try to use both together it doesn’t work well.
And I try to define opts like this:
opts=’–restart=always -d’
the message from docker is:
docker: Error response from daemon: invalid restart policy ‘always -d’, but the print message contains:
opts:–restart=always -d
Somebody removes --restart=
The problem was that, I used variables coming from other bash command in my script (like curl, ps etc). All of these variables end with carriage return \r. When I try to insert these variables into a docker parameter string \r are inside it. I need to add:
| sed 's/\r//' to all of these commands.
How can I run a command inside a docker container, using docker run, where bash variables are evaluated inside the container?
E.g.:
$ SOMEONE=host
$ docker run --env SOMEONE=busybox busybox echo "Hello $SOMEONE"
Hello host
How can I make it output Hello busybox?
To prevent the replacement from happening from the outer shell, one needs to use single quotes, not double.
To ensure that there is an inner shell that can do a replacement (echo doesn't have any such functionality itself!), we need to explicitly call sh -c; otherwise, Docker will just directly invoke execlp("echo", "echo", "$SOMEONE", NUL) inside the container, which doesn't actually do any substitution.
Thus:
docker run --env SOMEONE=busybox busybox sh -c 'echo "Hello $SOMEONE"'
Using docker run, where bash variables are evaluated inside
By far the easiest, non-cryptic approach is to write a bash function with all commands to be executed inside the container. Benefits:
Easy to write - no need to use special quote placement and escaping
Easy to debug - see what bash actually does inside the container
Easy to maintain - write readable scripts, not cryptic commands
Easy to write and maintain
Here's an example bash function that expands all variables inside a docker container.
-- (host) $ ./create-db.sh
#!/bin/bash
function main_inside_docker {
# all variables are expanded insider docker
DBNAME=${1:-testdb}
echo "creating database $DBNAME"
PATH=$MSSQL_PATH:$PATH
SQL="
create database $DBNAME;
select database_id, name, create_date from sys.databases;
"
sqlcmd -U SA -P $SA_PASSWORD -Q "$SQL"
}
# declare the function inside docker and run it there
CMD="$(declare -f main_inside_docker); main_inside_docker $#"
docker exec -it mssql bash -c "$CMD"
Essentially this declares the main_inside_docker function inside the container, then runs it with all arguments provided from the host invocation. All variables inside the function are expanded inside the docker container. The function just works the way one would expect.
Easy to debug
To debug the function, set "-x" as the first command in $CMD:
CMD="set -x; $(declare -f ...)"
When running it this way, it will print the bash trace from inside the container nicely:
(host) $ ./create-db.sh foodb
+ main_inside_docker
+ DBNAME=foodb
+ echo 'creating database foodb'
creating database testdb
...
I'm trying to create a script to run a docker cluster.
In my script there is a moment that I want to copy some files from the docker to my local machine. So I'm creating the CONTAINER_WORKDIR variable.
CONTAINER_WORKDIR=`docker exec -it jmeter-master /bin/pwd`
The value stored in CONTAINER_WORKDIR is:
/usr/local/apache-jmeter-3.2/bin
The problem is that there is a strange character in the end of this variable. Try to execute the line below:
echo "docker cp jmeter-master:$CONTAINER_WORKDIR/output.csv ."
My expected result is
docker cp jmeter-master:/usr/local/apache-jmeter-3.2/bin/output.csv .
But the real output is:
/output.csv .ter-master:/usr/local/apache-jmeter-3.2/bin
The pwd or the docker exec command is returning a returning character.
There is a way to remove this character from CONTAINER_WORKDIR variable
This script that executes what I presume must be
CONTAINER_WORKDIR=$(docker exec -it jmeter-master /bin/pwd)
may have been written with an editor that stores text files with DOS line-endings (like Notepad++).
Run dos2unix on that script, or use
$ tr -d '\r' <script >script-new
to fix it.
When I execute the following command (which moves all files with the .txt and .sbreaks extension to another folder):
sudo docker exec name mv xyz/data/outputs/*.{sbreaks,txt} <>/data/spare
I get the following error:
mv: cannot stat ‘xyz/data/outputs/*.sbreaks’: No such file or directory
mv: cannot stat ‘xyz/data/outputs/*.txt’: No such file or directory
But, when I go into docker via sudo docker exec -it name bash and execute the same command: mv xyz/data/outputs/*.{sbreaks,txt} xyz/data/spare, it executes fine.
What am I doing wrong here?
PS: Both local and the Docker container are ubuntu environments
That is because the * is expanded by a shell program (i.e. bash). (Psst, this is typical interview question).
So pass your command to a shell and let it launch the mv for you:
sudo docker exec cypher bash -c 'mv xyz/data/outputs/*.{sbreaks,txt} .......'
When you do docker exec some_program some_param, docker searches for some_program and executes it directly without doing anything extra, and just pass some_param as a parameter (a star in your case). mv expects real file names, and not *.