Get a Bash Scripts Absolute Path

While migrating an application from one CD process to another, I have been updating my deployment scripts for the application. Part of that has been updating the workflows and Dockerfiles, but also the actual scripts I use to start the docker containers themselves.

I wanted to make the new scripts are generic and reusable as possible so that they were not dependent on a path structure for linking to relatively linked files and paths. eg: A Docker volume mapping does not like relative paths, and because the script can be called from anywhere on the server, the pwd command is not a good solution. The realpath command is also not consistently available across all platforms.

I eventually came across this stackoverflow post, which gave me the solution I was looking for

#!/bin/bash
# /opt/deployment/restart.sh

SWD="$( cd -- "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
docker run -d \
    -p $THISPORTNO:$GUESTPORT \
    --env HOST_NAME=$CONTAINER \
    --restart always \
    --volume $SWD/data:/www/data \
    --log-opt max-size=1m \
    --log-opt max-file=3 \
    --name $CONTAINER \
    $IMAGENAME:$TAG || exit 1

The SWD variable is the absolute path to the file running containing the script.