CODEWITHSUNDEEP
postgresqlshelluser-management
m33lky
m33lky

Reputation: 7285

How to check if a postgres user exists?

createuser allows creation of a user (ROLE) in PostgreSQL. Is there a simple way to check if that user(name) exists already? Otherwise createuser returns with an error:

createuser: creation of new role failed: ERROR:  role "USR_NAME" already exists

UPDATE: The solution should be executable from shell preferrably, so that it's easier to automate inside a script.

Upvotes: 119

Views: 121148

Answers (7)

geoDev62
geoDev62

Reputation: 1

A complete snippet for PHP:

  • and furthermore, it might be better to mention the system catalog/table name "pg_roles" in front of the column name "rolname". Like this: "pg_roles.rolname".

  • and to mention it, because it confused me: it is really spelled "rolname" and not "rolename". 

// PHP Version 8.1.13
// PostgreSQL 15

try {
    // database connection
    $pdo = new PDO("pgsql:host=$host;port=$port;dbname=$dbname", $dbusername, $dbuserkeyword, [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION]);

    if ($pdo) { // went fine

        // a query to ask if user available in table (system catalog) "pg_roles" and column "rolname"
        $myResult = $pdo -> query("SELECT * FROM pg_roles WHERE pg_roles.rolname='{$theuseriamlookingfor}'");

        // retrieve the values from response in an Array
        $myResult = $myResult -> fetchAll();

        // output the first value from that Array
        echo $myResult[0]["rolname"];
    } 

} catch (PDOException $e) {
    // output the error-message
    echo $e->getMessage();
}

Upvotes: 0

gluttony
gluttony

Reputation: 569

Inspired from accepted answer, that unfortunately did not work for me (error on direct psql call), I then did something like this:

if ! echo "SELECT * FROM pg_roles WHERE rolname='USR_NAME'" | psql -h localhost -U postgres | grep -E "[1-9][0-9]* rows"; then
  # User not found, create it
  if ! echo "CREATE USER USR_NAME WITH PASSWORD 'USR_NAME' CREATEDB SUPERUSER" | psql -h localhost -U postgres; then
    echo "Error creating USR_NAME"
    exit 1
  fi
fi

Even if I think grep -E "1 rows" is safe here since we should not have more that one user of same name, I prefer keeping grep -E "[1-9][0-9]* rows" to get a generic "I got 1 or more result(s)" returning success. And I put exit 1 if it fails because I'm on a script that needs this user created to run properly.

Upvotes: 0

Michael Krelin - hacker
Michael Krelin - hacker

Reputation: 143249

SELECT 1 FROM pg_roles WHERE rolname='USR_NAME'

And in terms of command line (thanks to Erwin):

psql postgres -tXAc "SELECT 1 FROM pg_roles WHERE rolname='USR_NAME'"

Yields 1 if found and nothing else.

That is:

psql postgres -tXAc "SELECT 1 FROM pg_roles WHERE rolname='USR_NAME'" | grep -q 1 || createuser ...

Upvotes: 195

Ben Millwood
Ben Millwood

Reputation: 7011

To do this entirely within a single psql command:

DO $$BEGIN
IF NOT EXISTS (SELECT FROM pg_catalog.pg_roles WHERE rolname = 'USR_NAME')
THEN CREATE ROLE USR_NAME;
END IF;
END$$;

Upvotes: 6

Pascal Polleunus
Pascal Polleunus

Reputation: 2521

psql -qtA -c "\du USR_NAME" | cut -d "|" -f 1

[[ -n $(psql -qtA -c "\du ${1}" | cut -d "|" -f 1) ]] && echo "exists" || echo "does not exist"

Upvotes: 3

cmcc
cmcc

Reputation: 59

Hope this helps those of you who might be doing this in python.
I created a complete working script/solution on a GitHubGist--see URL below this code snippet.

# ref: https://stackoverflow.com/questions/8546759/how-to-check-if-a-postgres-user-exists
check_user_cmd = ("SELECT 1 FROM pg_roles WHERE rolname='%s'" % (deis_app_user))

# our create role/user command and vars
create_user_cmd = ("CREATE ROLE %s WITH LOGIN CREATEDB PASSWORD '%s'" % (deis_app_user, deis_app_passwd))

# ref: https://stackoverflow.com/questions/37488175/simplify-database-psycopg2-usage-by-creating-a-module
class RdsCreds():
    def __init__(self):
        self.conn = psycopg2.connect("dbname=%s user=%s host=%s password=%s" % (admin_db_name, admin_db_user, db_host, admin_db_pass))
        self.conn.set_isolation_level(0)
        self.cur = self.conn.cursor()

    def query(self, query):
        self.cur.execute(query)
        return self.cur.rowcount > 0

    def close(self):
        self.cur.close()
        self.conn.close()

db = RdsCreds()
user_exists = db.query(check_user_cmd)

# PostgreSQL currently has no 'create role if not exists'
# So, we only want to create the role/user if not exists 
if (user_exists) is True:
    print("%s user_exists: %s" % (deis_app_user, user_exists))
    print("Idempotent: No credential modifications required. Exiting...")
    db.close()
else:
    print("%s user_exists: %s" % (deis_app_user, user_exists))
    print("Creating %s user now" % (deis_app_user))
    db.query(create_user_cmd)
    user_exists = db.query(check_user_cmd)
    db.close()
    print("%s user_exists: %s" % (deis_app_user, user_exists))

Provides idempotent remote (RDS) PostgreSQL create role/user from python without CM modules, etc.

Upvotes: 2

matt
matt

Reputation: 1066

Following the same idea than to check if a db exists

psql -t -c '\du' | cut -d \| -f 1 | grep -qw <user_to_check>

and you can use it in a script like this:

if psql -t -c '\du' | cut -d \| -f 1 | grep -qw <user_to_check>; then
    # user exists
    # $? is 0
else
    # ruh-roh
    # $? is 1
fi

Upvotes: 13

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