My usual key sequence is:

quit()
quit
exit()
exit
q
q()
!q
^C
help
Alt + Tab
google.com
Quit PSQL
\q

I think veterans of the psql command line usually shorten that to just:

\q

Ctrl+D is what I usually use to exit psql console.

Use:

• Ctrl+Z - this sends the TSTP signal (TSTP is short for “terminal stop”)
• Ctrl+\ - this sends the QUIT signal

For curiosity:

• Ctrl+D - this sends the EOF character. EOF stands for "end of file". In this concrete case it exits from the psql subprogram, as the shell is waiting for user input. This should not be 'the way to go' as it is not working if:
• any other character is entered before - try entering some white spaces and then press Ctrl+D, it's not going to exit psql.
• if the user input is not required at all

quit or exit or \q

Based on PostgreSQL 11 Beta 1 Released!:

User Experience Enhancements

Another feature that fell into this category was the inability to intuitively quit from the PostgreSQL command-line (psql). There has been numerous recorded complaints of users trying to quit with the quit and exit commands, only to learn that the command to do so was \q.

We have heard your frustrations and have now added the ability to quit the command-line using the keywords quit and exit and hope that quitting a PostgreSQL session is now as enjoyable as using PostgreSQL.

I learned that I could include \q in a batch .sql file, so I could have psql quit earlier from an \i operation.

For Linux command line \q + enter.

Quiting with Ctrl + D also is works

Actually, \q, exit and CTRL + D did'nt worked for me to exit from the psql program.

Ctrl + Shift + D

Worked for me. Hope it ll help someone :)

My ubuntu version is 19.04