Performing queries on a Postgres docker container through a bash script - bash

Question

I'm working with a simple postgres database and docker. Currently, I have a docker-compose file which creates the container I need and loads in the SQL files. After loading in this data, I would like it to perform a simple query through a bash script that I"m going to use for some basic tests (i.e., confirm # of rows > 0, etc). To start, I'm just trying to make a simple script that will run and print the number of rows (then I can worry about implementing actual testing). Here is what I have so far:
docker-compose.yml:
services:
postgres:
image: postgres
environment:
POSTGRES_DB: test-db
POSTGRES_USER: postgres
POSTGRES_PASSWORD: postgres
volumes:
- ./database/create_table.sql:/docker-entrypoint-initdb.d/create_table.sql
- ./databases/data.sql:/docker-entrypoint-initdb.d/data.sql
- ./script/test.sh:/docker-entrypoint-initdb.d/test.sh
test.sh:
#!/bin/bash
echo "Accessing bash terminal of DB container"
docker exec -it postgres_1 bash
echo "Accessing psql terminal"
psql -U postgres
echo "Connecting to database"
\c database
echo "Checking number of rows"
numrows = $("SELECT count(*) FROM my_table")
echo numrows + " found."
Currently when I run docker-compose up, it creates the data from my SQL files and then stays idle. Is there something additional I need to run my script? I am able to do all of this myself through a separate terminal, but I would like this to all be automated so that I can just add tests to my test.sh and then run that rather than having to do it manually each time. What am I missing here? Shouldn't my script work since I really just recreated the commands I was executing manually? Thanks for any help!

Answer 1

By the time your bash script is executed you are already in the postgres container itself. So, you can simply query the database from there - as #DavidMaze already pointed out. Your script might look like this:
#!/bin/bash
db_name='test-db'
db_user='postgres'
function execute_sql() {
psql --tuples-only -U $db_user -d $db_name -c "$#"
}
function log() {
printf "Log [%s]: %s\n" "$(date --iso-8601=seconds)" "$*"
}
numrows=$(execute_sql "SELECT count(*) FROM my_table")
log "${numrows} rows found"
Output should be something like that:
postgres_1 | /usr/local/bin/docker-entrypoint.sh: sourcing /docker-entrypoint-initdb.d/test.sh
postgres_1 | [2020-03-31T23:02:14+00:00]: 4 rows found
Regarding the testing: If you only want to run SQL queries and don't do/need additional scripting you can simply put your SQL test queries into a .sql file (e.g. test.sql) as well.
One more important thing to mention - which I'm sure you already know: The files (*.sql, *.sh etc.) that you mount to the postgres container are executed in alphabetical order, i.e.
create_table.sql
data.sql
test.sh
So, you are good.