How to display Postgres version in the CLI pompt?

I whish to display the version of the server I am connected to in the command-line (console) interface prompt. From what I read in the documentation, it is possible to execute a shell command, it is possible to display a psql variable value.

The idea is to get the server's version information on connection and use it in the client's prompt. How can I (in the .psqlrc file ?) assign the server version in a psql variable ?

Edit: Jack Douglas♦ has the right answer by pointing out the \gset feature. It ended up with a

show server_version
\gset
\set PROMPT1 '%:server_version: >'

Thank you.

Since 9.3, you can do this using \gset in psqlrc:

select split_part(version(),' ',2) pmt
\gset
\set PROMPT1 '%:pmt:'

Or, as 'the value of the selected prompt variable is printed literally, except where a percent sign (%) is encountered':

select split_part(version(),' ',2) "PROMPT1"
\gset

If your version is <9.3, it's still possible, but much uglier, e.g. something like:

\set PROMPT1 `psql postgres postgres -Atc "select split_part(version(),' ',2)"`

StackExchange Database Administrators Q#111780, answer score: 8