For example, to change the number of shell commands saved in the history list, you need to set the shell variable history. It is set to 100 by default, but you can increase this if you wish.
set history = 200
Check this has worked by typing
echo $history
However, this has only set the variable for the lifetime of the current shell. If you open a new xterm window, it will only have the default history value set. To PERMANENTLY set the value of history, you will need to add the set command to the .cshrc file.
First open the .cshrc file in a text editor. An easy, user-friendly editor to use is nedit.
nedit ~/.cshrc
Or if you don't have it installes you can use vi text editor.
vi ~/.cshrc
Add the following line AFTER the list of other commands.
set history = 200
If you are using vi:
set history = 200
<ESC> (for going to the command mode)
:w (for saving)
:q (for exit the programm)
Save the file and force the shell to reread its .cshrc file buy using the shell source command.
source .cshrc
Check this has worked by typing
echo $history