watch in PostgreSQL with clear screen (cos) - postgresql

Question

\watch command is great in Postrges.
It appends an output of a query, being watched over and over.
For example, when I previously run a query SELECT id, nickname FROM users;, and entered \watch, in case of no new data, I get the same output over and over:
my_db=# SELECT id, nickname FROM users;
id | nickname
----+----------
1 | AntonAL
(1 row)
my_db=# \watch
четверг, 31 августа 2017 г. 13:23:26 (every 2s)
id | nickname
----+----------
1 | AntonAL
(1 row)
четверг, 31 августа 2017 г. 13:23:28 (every 2s)
id | nickname
----+----------
1 | AntonAL
(1 row)
It there any option to clear screen output, between watch executions?
I want to get dashboard-like experience, when a set of rows is displayed and refreshed, not appended over and over to the Postgres console output.

Answer 1

I had this problem, and with a suggestion from MatheusOl on #postgresql, the following works for me:
\C `clear`
SELECT * FROM pg_tables \watch 10
The \C [value] command sequence lets you set a title, and you can set that (shelling out with backticks) to the ANSI escapes returned by clear.

Answer 2

I don't think psql has any way to clear the terminal. Maybe do with bash?
while true;
clear;
psql -c "SELECT id, nickname FROM users"
sleep 2;
done

Answer 3

Similar to the last answer but a little simpler with the "watch" command (on linux) :
watch 'psql -c "SELECT id, nickname FROM users"'
... this will execute the query with psql every 2 seconds (default interval) and you can also add different parameters to this command :
$ watch --help
Usage:
watch [options] command
Options:
-b, --beep beep if command has a non-zero exit
-c, --color interpret ANSI color and style sequences
-d, --differences[=<permanent>]
highlight changes between updates
-e, --errexit exit if command has a non-zero exit
-g, --chgexit exit when output from command changes
-n, --interval <secs> seconds to wait between updates
-p, --precise attempt run command in precise intervals
-t, --no-title turn off header
-x, --exec pass command to exec instead of "sh -c"
-h, --help display this help and exit
-v, --version output version information and exit
For more details see watch(1).
I like to use this to monitor sessions activity with pg_stat_activity :
$ cat sessions.sql
select pid as process_id,
usename as username,
datname as database_name,
client_addr as client_address,
application_name,
backend_start,
state,
state_change
from pg_stat_activity;
$ watch -d psql -f sessions.sql
... and we get this output refreshed every 2 seconds :
Every 2.0s: psql -f sessions.sql Sun Sep 29 17:38:20 2019
process_id | username | database_name | client_address | application_name | backend_start | state | state_change
------------+----------+---------------+----------------+------------------+-------------------------------+--------+-------------------------------
1240 | postgres | | | | 2019-09-29 15:40:36.697364-04 | |
1236 | | | | | 2019-09-29 15:40:36.697681-04 | |
14025 | postgres | postgres | | psql | 2019-09-29 17:38:20.508996-04 | active | 2019-09-29 17:38:20.511069-04
1233 | | | | | 2019-09-29 15:40:36.69497-04 | |
1232 | | | | | 2019-09-29 15:40:36.695851-04 | |
1234 | | | | | 2019-09-29 15:40:36.690183-04 | |
(6 rows)