You can just use an sh to execute the command. If you are using declarative syntax (starting with pipeline instead of node) I'd suggest to do that in the environment, so you can read the result in all stages of your pipeline:
environment {
COMMIT = sh(script: '{ git log -1 --pretty=format:\'%an\'; echo "@xyzcompany.com, developer@xyzcompany.com"; } | xargs -I{} echo {} | sed \'s/\n//\'', returnStdout: true).trim()
}
Or –if you use scripted syntax– you just declare a variable:
def commit = sh(script: '{ git log -1 --pretty=format:\'%an\'; echo "@xyzcompany.com, developer@xyzcompany.com"; } | xargs -I{} echo {} | sed \'s/\n//\'', returnStdout: true).trim()