clear terminal critical outputs

Question

I have Ubuntu 18.04 on my win10, and I usually create my password with this line of code:

echo -n "<some text generated by hand from the site's domains>" | sha256sum |cut -c-20 

But today I accidentally pressed Enter after the echo command.

Does Ubuntu save its terminal outputs in a file? Am I safe just using the clear command?

Do you guys recommend a better solution so my password is different from each other and hard to compute a new one based on some of my other passwords?

Thanks.

Answer 1

The output of the command is usually not stored anywhere and closing the window is enough. But the command itself is stored: in the shell's history.

To remove it from there it is best to first close all terminal windows. Normally, the history is written to the file ~/.bash_history when the shell ends and directly manipulating the file won't help because it gets overwritten upon shell's exit. There are ways to configure history differently but the easiest is to simply close all terminal windows.

Now open one new terminal window and type

history

or

history | grep echo

Sample output:

...
2007  echo -n "<some text generated by hand from the site's domains>" | sha256sum |cut -c-20 
2008  echo -n "secret" | sha256sum |cut -c-20 
2009  echo -n "secret"
2010  history

Here you see that not only the "malicious" command is stored but also the "correct" one. You can delete it with

history -d 2009

where 2009 is the number in the first column. Change that appropriately. Now:

history
...
2007  echo -n "<some text generated by hand from the site's domains>" | sha256sum |cut -c-20 
2008  echo -n "secret" | sha256sum |cut -c-20 
2009  history
2010  history -d 2009
2011  history

For the future you might want to prefix your echo … | sha256sum … with a space, i.e.

_echo -n "secret" | sha256sum |cut -c-20   # The '_' indicates a leading space

This way the complete command won't be recorded in the history. The behaviour is controlled by the HISTCONTROL variable (man bash):

HISTCONTROL

A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes ignorespace, lines which begin with a space character are not saved in the history list. A value of ignoredups causes lines matching the previous history entry to not be saved. A value of ignoreboth is shorthand for ignorespace and ignoredups.

You may want to add export HISTCONTROL='ignoreboth' to your ~/.bashrc to achieve that.