Shell features you didn't know you needed (or possibly even existed) #9

I came across this one needing to turn a Git branch name into a Docker image tag, and having it trip over the fact that our branch naming convention is <user>/<issue>/<short description>, and Docker doesn't like / in tags. Obviously there are many ways of stripping/substituting the /: for example, using tr IMAGE_TAG=$(echo $BRANCH | tr \/ \-) using sed IMAGE_TAG=$(echo $BRANCH | sed -e 's/\//-/g') using perl IMAGE_TAG=$(echo $BRANCH | perl -pe 's/\//-/g') And there's probably others with awk, and who knows what else. But why bother, when you can do it in bash itself. IMAGE_TAG=${BRANCH//\//-} To clarify, that's essentially: ${VARIABLE/from/to} # replace first occurrence of 'from' ${VARIABLE//from/to} # replace all occurrences of 'from' Simple, when you know how.