export NAME=value
export means to move the variable from the shell into the
environment. This means that programs other than the shell (for
instance, a file viewer) will be able to access it.
echo $PAGER
This is the easiest way to see the value of a variable. $PAGER tells
the shell to insert the value of the PAGER variable _before_
invoking the command. echo echoes back its argument: in this case,
it echoes the current PAGER value, less.
man more
Displays the more manual. This time, man should have invoked the
less pager.
less has lots of features that more lacks. For example, you can
scroll backward with the b key. You can also move up and down (even
sideways) with the arrow keys. less won’t exit when it reaches the
end of the man page; it will wait for you to press q.
You can try out some less-specific commands, like b, to verify that
they don’t work with more and that you are indeed using more.
unset PAGER
If you don’t want to specify a pager anymore, you can unset the
variable. man will then use more by default, just as it did before
you set the variable.
echo $PAGER
Because PAGER has been unset, echo won’t print anything.
PS1=hello:
Just for fun, change your shell prompt. $ should now change; see
Figure 6.2 for details.
export is not necessary, because you’re changing the shell’s own
behavior. There’s no reason to export the variable into the
environment for other programs to see. Technically, PS1 is a _shell
variable_ rather than an environment variable.
If you wanted to, you could export the shell variable, transforming
it into an environment variable. If you do this, programs you run
from the shell can see it.