/usr/bin/pg_archivecleanup

pg_archivecleanup removes older WAL files from PostgreSQL archives.

Usage:
  pg_archivecleanup [OPTION]... ARCHIVELOCATION OLDESTKEPTWALFILE

Options:
  -d             generate debug output (verbose mode)
  -n             dry run, show the names of the files that would be removed
  -V, --version  output version information, then exit
  -x EXT         clean up files if they have this extension
  -?, --help     show this help, then exit

For use as archive_cleanup_command in postgresql.conf:
  archive_cleanup_command = 'pg_archivecleanup [OPTION]... ARCHIVELOCATION %r'
e.g.
  archive_cleanup_command = 'pg_archivecleanup /mnt/server/archiverdir %r'

Or for use as a standalone archive cleaner:
e.g.
  pg_archivecleanup /mnt/server/archiverdir 000000010000000000000010.00000020.backup

Report bugs to <pgsql-bugs@lists.postgresql.org>.