rev(1) on FreeBSD
The text 420dbddc7138, as FreeBSD 4.11-RELEASE, FreeBSD 4.10-RELEASE, FreeBSD 4.9-RELEASE, FreeBSD 4.8-RELEASE, FreeBSD 4.7-RELEASE, FreeBSD 4.6.2-RELEASE, FreeBSD 4.6-RELEASE, FreeBSD 4.5-RELEASE, FreeBSD 4.4-RELEASE, FreeBSD 4.3-RELEASE shipped it.
reverse lines of a file