I'm using this in a service declartion:ExecStartPre=/usr/bin/docker pull $DOCKER_USERNAME/redis-replication:latestIn the log of systemd, I can see this when I try to start the service:Usage: docker pull [OPTIONS] NAME[:TAG]Pull an image or a repository from the registry-a, --all-tags=false    Download all tagged images in the repositoryIt looks like systemd didn't execute the proper command but some weird one.What could it be and how to correct that?Edited: Here's my entire unit file[Unit]Description=Run redis replicationAfter=docker.serviceRequires=docker.service[Service]Restart=alwaysRestartSec=10sEnvironmentFile=/etc/vax/credentialsEnvironmentFile=/etc/vax/centos-ipEnvironmentFile=/etc/vax/docker-authEnvironmentFile=/etc/vax/cluster-prefixExecStartPre=-/usr/bin/docker kill redisrepExecStartPre=-/usr/bin/docker rm redisrepExecStartPre=/usr/bin/docker pull $DOCKER_USERNAME/redis-replication:latestExecStart=/usr/bin/docker run --rm --name redisrep    -v /var/data/myproject/redis:/data    -e S3_ACCESS_KEY=$S3_ACCESS_KEY    -e S3_SECRET_KEY=$S3_SECRET_KEY    -e S3_BUCKET=$S3_BUCKET    -e BACKUP_PREFIX=$BACKUP_PREFIX    -e REPLICATE_FROM_IP=$CENTOS_IP    -e REPLICATE_FROM_PORT=6379    $DOCKER_USERNAME/redis-replication:latestExecStop=/usr/bin/docker kill redisrep[X-Fleet]MachineMetadata=machineIndex=1
How to use quote and dollarsign with systemd
systemd
After some research around, I found that it's ok to use quote in ExecStart definition of a systemd service file. As for using shell variable, it's necessary to use curly braces to clarify where the variable name end when non-space characters is connected to the variable itself. In the above case, the system must have treat $DOCKER_USERNAME/redis as the variable name instead of $DOCKER_USERNAME. Add a curly braces then it is interpreted correctly.Edit: More information about what syntax is ok with systemd can be found here: http://www.freedesktop.org/software/systemd/man/systemd.service.html#Command%20linesBasically most shell notation is ok, with the except of pipe operators.