On a standard installation the Bash history gets overwritten when multiple sessions of it are used. Using multiple sessions is a very common way of working so this is probably a problem recognised by many users.
By executing this script during login, all commands executed through Bash will be kept forever in the file $HOME/.persistent_history.
The code to make Bash history persistent is borrowed from a great blog post written by Eli Bendersky at:
http://eli.thegreenplace.net/2013/06/11/keeping-persistent-history-in-bash.
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Put the file phist.sh at a place you find convenient, e.g. in the directory $HOME/phist/.
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To make the script run when you login, add this line somewhere in your $HOME/.bashrc file:
source $HOME/phist/phist.sh -
A few aliases and environment variables are now setup to enable persistent history.
The commands you run through Bash will now be saved into the file $HOME/.persistent_history. All Bash sessions share this single file.
Each Bash session does have its own history as before. When you use the history command or use the up/down arrows, you will only see the history that belongs to the current session.
If you want to see the global and persistent history you should run the phist alias which is defined by installing this script. It will give you the 500 latest written commands.
When you know you have used sed some time ago to remove trailing whitespace in a file, just type:
phgrep sed
The command line for that command will then be shown for you.
This alias is also defined for your convenience. It searches the history that belongs to the current Bash session only.