create db if not exists in postgres .sh file - postgresql

Question

I want to execute these lines in the below .sh file:
#!/bin/sh +x
sudo su postgres
psql -U postgres -tc "SELECT 1 FROM pg_database WHERE datname = 'test_db'" | grep -q 1 || psql -U postgres -c "CREATE DATABASE test_db"
But only 'sudo su postgres' is executing and the 2nd line is not executing. Can someone help me execute those 2 lines

Answer 1

Just pass your psql command to su:
sudo su postgres -c "psql -U postgres -tc \"SELECT 1 FROM pg_database WHERE datname = 'test_db'\" | \
grep -q 1 || psql -U postgres -c \"CREATE DATABASE test_db\""
If you want to pass the datname value as a parameter, replace it by $1 in the script ($1, $2, etc. expand as the first, second, etc. parameters you pass to your script):
sudo su postgres -c "psql -U postgres -tc \"SELECT 1 FROM pg_database WHERE datname = '$1'\" | \
grep -q 1 || psql -U postgres -c \"CREATE DATABASE $1\""
and call your script like this:
./script.sh test_db
You can even have optional parameters. For instance, if you want an optional parameter for the table name (pg_database in your example):
db=pg_database
if [ -n "$2" ]; then db="$2"; fi
sudo su postgres -c "psql -U postgres -tc \"SELECT 1 FROM $db WHERE datname = '$1'\" | \
grep -q 1 || psql -U postgres -c \"CREATE DATABASE $1\""
and call your script like this:
./script.sh test_db
to use the default, else:
./script.sh test_db other_pg_database

Answer 2

I suggest you update your sudo configuration so you can directly express that you only need to as postgres and not root:
sudo -u postgres ...
For example:
user host = (postgres) command
where user is your user, host is the host name you want this apply (ALL?), and command is the name of your command (ALL?) possible prefixed with "NOPASSWD: " if you don't want to require a password.
Then do the action and deal with the error if needed instead of guarding against it:
sudo -u postgres bash -c "psql -U postgres -c "CREATE DATABASE $1"
Possible single quoting the $1 and if you want that to be robust, escape any single quotes in the database name. I showed you a shell (bash) in the above, so can easily tag on error handling.