On a Debian system, one can type
pager in order to use whatever pager program happens to be default/available. By default,
less is used, and if not available, the lesser
more gets to do the job. Is such a thing available in other Unix and Linux systems?
The unix tradition is for applications that want to call a pager to call
$PAGER, i.e. use the contents of the environment variable
PAGER as a command name. (Whether shell metacharacters are expanded in
$PAGER is not consistent between applications.) The unix tradition further uses
more if the
PAGER variable is not set. There is a similar tradition for text editors: use
$EDITOR (or, for historical reasons,
$VISUAL), falling back to
Having a command named
pager is specific to Debian (and derivatives, including Ubuntu).
/usr/bin/pager is in fact a symbolic link to
/etc/alternatives/pager, which points to the the “best” available pager (the Debian maintainers decide which is best, and the system administrator can override their choice), using the alternatives framework.
Debian also provides
/usr/bin/sensible-pager. This script runs
$PAGER if the variable is set, and falls back to
pager otherwise. Its purpose is to be used in programs where a single pager path has to be hard-coded. This behavior is documented in the Debian policy manual.