Less

Less is a command-line pager: a program that shows one page out of a file in a terminal window and shows more pages one at a time upon user request, irrespective of file size. Another noted similar program is more.

Less allows moving back and forth, supports arrow keys, and, when at the end of a pipeline, shows as much of the buffer as it can from the content fed into it, refreshing its buffer regularly as the pipeline provides more of the content.

Examples:
 * less --help
 * Displays help in the less command itself. -h and -H do not output help.
 * less --version
 * less -V
 * Outputs version.
 * less -psearchterm MyFile.txt
 * Option -p opens the files at the occurrences of the searchterm.
 * grep dog AnimalData.txt | less

Keyboard commands
Keyboards commands that can be used once less is started:
 * up and down arrow keys - scroll up or down
 * page up or page down - as expected
 * home - go to the top of the file
 * end - go to the bottom of the file
 * space - scroll forward
 * q - quit
 * h - help
 * / - forward regex search
 * n - next occurrence of a search match
 * N - previous occurrence of a search match
 * -i - ignore case in further searches

Links:
 * less man page - section COMMANDS, freebsd.org

Versions
Versions of GNU less can be seen in http://ftp.gnu.org/gnu/less/.

Greenwood Software less versions can be seen in http://www.greenwoodsoftware.com/less/download.html and http://www.greenwoodsoftware.com/less/old.html.

A version of less for MS Windows is available from GnuWin32 project, as well as from Cygwin.

License
Less is dual-licensed under GNU GPL V3+ and The Less License, a BSD-like license. It follows from README file from less-481.tar.gz GNU less distribution. The Less License is stated in the LICENSE file in the same distribution.