You can look back at all of the previous Terminal commands within Terminal by typing in
history. This gives you a list of ever Terminal command you have entered. This list can get very long and you may, at some point, want to clear the list to trim it down and remove the amount of entries. This is a good way of starting afresh or deleting wrong or incorrect commands.
Cleaning Up The List
To clean up the list open Terminal and type the following:
The -c option is the clear option. This will clear the history file completely. You now have a blank history file.
Its is a quick, simple trick to clean up the file. Currently my history file has 3000 entries which is a fair few.