  Emoji is becoming a ubiquitous language and gaining worldwide popularity in
recent years including the field of software engineering (SE). As nonverbal
cues, emojis are widely used in user understanding tasks such as sentiment
analysis, but few work has been done to study emojis in SE scenarios. This
paper presents a large scale empirical study on how GitHub users use emojis in
development-related communications. We find that emojis are used by a
considerable proportion of GitHub users. In comparison to Internet users,
developers show interesting usage characteristics and have their own
interpretation of the meanings of emojis. In addition, the usage of emojis
reflects a positive and supportive culture of this community. Through a manual
annotation task, we find that sentimental usage is a main intention of using
emojis in issues, pull requests, and comments, while emojis are mainly used to
emphasize important contents in README. These findings not only deepen our
understanding about the culture of SE communities, but also provide
implications on how to facilitate SE tasks with emojis such as sentiment
analysis.
