The command-line PostgreSQL database client keeps a command history.
Much like on a Linux console, you can use the up arrow to scroll back through previous commands. This can be handy if you want to repeat a command, or to change a parameter on a long query.
One other thing that is less widely-known is that you can view the ENTIRE history by typing “\s”. Backslash-s will function pretty much the same as the Linux “history” command, and can give you multiple pages of commands.
Much like the history of the Bash shell, the Postgres command history is stored in your home directory in the hidden file .psql_history. Although this is handy, it can also be a security risk to keep old commands where prying eyes can find them. You can easily delete this file, or clear it using the command:
truncate -s 0 .psql_history
I like the truncate command because it’s a nice, clean, one-step way to clear a file without deleting it.