How to remove a single line from history?

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

Additionally, if the line you want to delete has already been written to your $HISTFILE (which typically happens when you end a session by default), you will need to write back to $HISTFILE, or the line will reappear when you open a new session:

history -w

1. To clear all your history, use

   history -c
   

2. To delete a single line, use

   history -d linenumber
   

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

function forget() {                                                              
   history -d $(expr $(history | tail -n 1 | grep -oP '^ \d+') - 1);              
}