I'm working in Mac OSX, so I guess I'm using bash...?

Sometimes I enter something that I don't want to be remembered in the history. How do I remove it?

Preventative measures

If you want to run a command without saving it in history, prepend it with an extra space

prompt$ echo saved
prompt$ echo not saved 
> # ^ extra space

For this to work you need either ignorespace or ignoreboth in HISTCONTROL. For example, run

HISTCONTROL=ignorespace

To make this setting persistent, put it in your .bashrc.

Post-mortem clean-up

If you've already run the command, and want to remove it from history, first use

history

to display the list of commands in your history. Find the number next to the one you want to delete (e.g. 1234) and run

history -d 1234

1. 
   

   To clear all your history, use

   
   
   

   history -c
   

   
   


2. 
   

   To delete a single line, use

   
   
   

   history -d linenumber
   

   
   

You always can edit and remove entries from ~/.bash_history, useful when you want to remove either one entry or more than one entry

I have this in my ~/.bashrc, which makes the command $ forget delete the previous command from history

function forget() grep -oP '^ d+') - 1); 

If you want to forget the entire bash session, you can kill the current bash process. Since the variable $$ hold the pid of the current shell, you can do:

kill -9 $$

You need to write the changes after you cleared the history. And if you wouldn't like to have the history wipe command in your history then you need to run the command like that:

history -c && history -w && logout

Good luck.

Adding another point suppose if you want to delete a range of history lines

You can use below script. 

Below example will delete history output from line 1 to line 150.

for i in `history | awk 'NR > 1 && NR <=150print $1'`; do history -d $i; done