[HACKERS] Contrib: pqasyncnotifier.c -- a shell command client for LISTEN

psql(1) does not output notifications asynchronously, as it does not
check for them when idle.  This makes it difficult to script handling of
NOTIFYs.

Attached is pqasyncnotifier.c, a simple command that allows one to
handle NOTIFYs asynchronously.

Cheers,

Nico
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