rlog

rlog is a command-line tool used to retrieve change history from revision-control repositories, primarily associated with the Revision Control System (RCS) and the Concurrent Versions System (CVS). It reads RCS files or CVS repository metadata and outputs log information for one or more files, or for entire modules. The output typically includes the revision numbers, authors, dates, and the log messages submitted with each revision. rlog can summarize history across multiple files and across branches, and it can filter results by revision ranges, date ranges, or other criteria depending on the implementation.

Because rlog accesses historical data without modifying the repository, it is a read-only operation. It is commonly used to audit changes, track authorship, and gather release notes or documentation of changes. In CVS workflows, rlog complements other commands such as co (checkout) and update by providing an overview of changes rather than the current working copy.

Rlog originated with the RCS tool chain in the 1980s and became part of CVS tooling. Modern distributed version control systems like Git have largely supplanted CVS, and rlog usage is now specialized in legacy projects or environments where CVS/RCS tooling remains in use. Some CVS clients provide a remote mode of rlog to fetch logs from repositories over a network.