env/index.js

const core = require('@actions/core');

function slugify(str) {
    str = str.replace(/^\s+|\s+$/g, ''); // trim
    str = str.toLowerCase();

    str = str.replace(/[^a-z0-9 -]/g, '') // remove invalid chars
             .replace(/\s+/g, '-') // collapse whitespace and replace by -
             .replace(/-+/g, '-'); // collapse dashes

    return str;
}

// https://help.github.com/en/actions/automating-your-workflow-with-github-actions/using-environment-variables#default-environment-variables
try {
    splitted_github_repository = process.env.GITHUB_REPOSITORY.split('/'); // octocat/Hello-World
    core.exportVariable('GITHUB_REPO_OWNER', slugify(splitted_github_repository[0]));
    core.info(`Set GITHUB_REPO_OWNER=${process.env.GITHUB_REPO_OWNER}`);
    core.exportVariable('GITHUB_REPO_NAME', slugify(splitted_github_repository[1]));
    core.info(`Set GITHUB_REPO_NAME=${process.env.GITHUB_REPO_NAME}`);

    splitted_github_ref = process.env.GITHUB_REF.split('/'); // refs/heads/feature-branch-1
    core.exportVariable('GITHUB_BRANCH_NAME', slugify(splitted_github_ref[2]));
    core.info(`Set GITHUB_BRANCH_NAME=${process.env.GITHUB_BRANCH_NAME}`);
} catch (error) {
    core.setFailed(error.message);
}