Multiline command : comment out one line

You can't comment out a piece of a line.

Note that since the newlines are escaped, the command is actually a single line (to the shell parser), and there's no way to comment out a part of a single line (except for at the very end).

Instead, maybe just make a copy of the original command in an editor and comment it out completely while keeping the modified command uncommented:

docker run \
 --rm \
 -u root \
 -v jenkins-data:/var/jenkins_home \
 -v /var/run/docker.sock:/var/run/docker.sock \
 -v "$HOME":/home \
 jenkinsci/blueocean

# Was originally:
# docker run \
# --rm \
# -u root \
# -p 8080:8080 \
# -v jenkins-data:/var/jenkins_home \
# -v /var/run/docker.sock:/var/run/docker.sock \
# -v "$HOME":/home \
# jenkinsci/blueocean

---

Alternatively, if you want to occasionally delete or change the -p option and its argument (assuming bash or a shell with the same array syntax):

port=( -p 8080:8080 )

docker run \
 --rm \
 -u root \
 "${port[@]}" \
 -v jenkins-data:/var/jenkins_home \
 -v /var/run/docker.sock:/var/run/docker.sock \
 -v "$HOME":/home \
 jenkinsci/blueocean

Then just change or comment out the assignment to port.

Taking this further:

docker_run_args=(
    --rm 
    -u root 
    -p 8080:8080 
    -v jenkins-data:/var/jenkins_home 
    -v /var/run/docker.sock:/var/run/docker.sock 
    -v "$HOME":/home 
    jenkinsci/blueocean
)

docker run "${docker_run_args[@]}"

Inside the array assignment, there are no issues with commenting out a line:

docker_run_args=(
    --rm 
    -u root 
#    -p 8080:8080 
    -v jenkins-data:/var/jenkins_home 
    -v /var/run/docker.sock:/var/run/docker.sock 
    -v "$HOME":/home 
    jenkinsci/blueocean
)

docker run "${docker_run_args[@]}"

You could substitute an empty command substitution:

docker run \
 --rm \
 -u root \
 $(: -p 8080:8080 ) \
 -v jenkins-data:/var/jenkins_home \
 -v /var/run/docker.sock:/var/run/docker.sock \
 -v "$HOME":/home \
 jenkinsci/blueocean