The commands executed in the terminal prefixed with blank space(s) are not recorded in the command history file. But is there a way to get the reverse i.e. the history should only record those which are prefixed with space?
You can reverse the default Ubuntu settings by setting two variables (HISTIGNORE an HISTCONTROL), use the commands like below:
HISTIGNORE='!( *)'
HISTCONTROL=ignoredups
HISTCONTROL=ignoredups changes history behaviour to only ignore duplicate lines, and not ignore lines starting with a space. (You can also set HISTCONTROL to the empty string (with HISTCONTROL= ) if you do want to keep duplicates, but that is usually not wanted.)
HISTIGNORE='!( *)' makes history ignore every line which doesn't start with a space: ( *) would match every line starting with a space, but the leading ! negates the match, so it matches everything which doesn't start with a space. And everything what is matched by the HISTIGNORE pattern will be ignored by history. (This latter option requires that bash is run with extglob turned on, with shopt -s extglob, but that is the default setting on Ubuntu.)
If you want to make this permanent, don't forget to put the above two commands into your ~/.bashrc.
