Store `docker run` command output in BASH variable

Question

I'm having an issue storing the output of docker run -it -d -p 43211:3000 --name appname -h hostname -v $PWD/local_dir:/root/remote_dir repo/imagename in a BASH varibale. I tried `backticks`, I also tried running it like the official docs say BASH_VAR=$(docker run ...), I even tried storing the output in a file with docker run --...>$FILE_DESCRIPTOR, but no luck storing the error situation, the situation when the name is already used by another container, like so:

$ FATA[0000] Error response from daemon: Conflict. The name "appname" is already in use by container 7c84d8d703c8. You have to delete (or rename) that container to be able to reuse that name.

I want to say that it works for the success situation, so I'm able to store in BASH_VAR the full container ID, upon running the application successfully, but unfortunately this solves only half the problem I'm facing.

Any help would be appreciated.

Thanks!

Anaesthesiology

does output=$(docker run -it -d -p 43211:3000 --name appname -h hostname -v $PWD/local_dir:/root/remote_dir repo/imagename 2>&1) work for you? 2>&1 redirects stderr to stdout. – Luminous

Thank you, kind sir! Yes, @kek2mgl, it worked like a charm! The reason I need this is because I'm building an interactive docker container management bash script, with Dialog and I need to parse the output of all commands I issue behind the scenes. You can answer the question so I can mark your comment as being the right answer. – Anaesthesiology

I have bash script like this '#!/usr/bin/bash result=$(docker run -e 'SITE=WL' -h pingnet --name pingnet --rm pingnet 2>&1) echo ${result}' and doesnt display any result – Reluctivity

Maybe the issue comes from the non interactivity of your terminal. You can try with the command script to emulate an interactive terminal. – Peristyle

Answer 1

What you need is to capture standard error and store it in a variable.

Using

BASH_VAR=$(command)

or

BASH_VAR=`command`

will capture standard output and not standard error.

This is the right syntax to store standard error messages in a variable:

BASH_VAR=$( { command; } 2>&1 )

Mastectomy

Answer 2

You could use a while loop to read each line of output as it's produced and do something with it that way.

while read -r line_of_output; do
  echo "line: $line_of_output"

done < <(docker ... 2>&1)

Also, if you're writing an interactive script, you might want to check out the select bash builtin

$ help select
select: select NAME [in WORDS ... ;] do COMMANDS; done
     Select words from a list and execute commands.

Sarasvati

Answer 3

you might need to break out of the while loop , but yes it is possible, example:

  MYSQL_IMAGE_NAME='mysql/mysql-server:5.7'
  docker pull "$MYSQL_IMAGE_NAME"
  docker images
  docker run --name=mysql-server-container -d "$MYSQL_IMAGE_NAME"
  docker container ls

  while read -r line ; do
     GENERATED_PWD="$(echo $line | grep 'GENERATED ROOT PASSWORD'|awk '{print $5}')"
     test -z $GENERATED_PWD || break
  done < <(docker logs --tail 3000 --follow mysql-server-container)
  echo "GENERATED_PWD: $GENERATED_PWD"

Extremely