pre-commit — Notification just prior to commit completion.
The pre-commit hook is run just
          before a commit transaction is promoted to a new revision.
          Typically, this hook is used to protect against commits that
          are disallowed due to content or location (e.g., your
          site might require that all commits to a certain branch
          include a ticket number from the bug tracker, or that the
          incoming log message is nonempty).
If the pre-commit hook program
          returns a nonzero exit value, the commit is aborted, the
          commit transaction is removed, and anything printed to
          stderr is marshalled back to the client.
The command-line arguments passed to the hook program, in order, are:
Repository path
Commit transaction name
Additionally, Subversion passes any lock tokens provided
          by the committing client to the hook script via standard
          input.  When present, these are formatted as a single line
          containing the string LOCK-TOKENS:,
          followed by additional lines—one per lock
          token—which contain the lock token information.  Each
          lock token information line consists of the URI-escaped
          repository filesystem path associated with the lock,
          followed by the pipe (|) separator
          character, and finally the lock token string.