What is the use of the '$' symbol (after branch=, sha_short= and commit_date=) in the below code for extracting the commit id details in a Github action workflow run on ubuntu
- name: Extract the commit ID
id: vars
shell: bash
run: |
echo "branch=${GITHUB_REF#refs/heads/}" >> $GITHUB_OUTPUT
echo "sha_short=$(git rev-parse --short "$GITHUB_SHA")" >> $GITHUB_OUTPUT
echo "commit_date = $(git show -s --format=%cd --date=short)" >> $GITHUB_OUTPUT