Check if database exists in PostgreSQL using shell

Question

I was wondering if anyone would be able to tell me about whether it is possible to use shell to check if a PostgreSQL database exists?

I am making a shell script and

Answer 1

The following shell code seems to work for me:

if [ "$( psql -tAc "SELECT 1 FROM pg_database WHERE datname='DB_NAME'" )" = '1' ]
then
    echo "Database already exists"
else
    echo "Database does not exist"
fi

Answer 2

kibibu's accepted answer is flawed in that grep -w will match any name containing the specified pattern as a word component.

i.e. If you look for "foo" then "foo-backup" is a match.

Otheus's answer provides some good improvements, and the short version will work correctly for most cases, but the longer of the two variants offered exhibits a similar problem with matching substrings.

To resolve this issue, we can use the POSIX -x argument to match only entire lines of the text.

Building on Otheus's answer, the new version looks like this:

psql -U "$USER" -lqtA | cut -d\| -f1 | grep -qFx "$DBNAME"

That all said, I'm inclined to say that Nicolas Grilly's answer -- where you actually ask postgres about the specific database -- is the best approach of all.

Answer 3

You can create a database, if it doesn't already exist, using this method:

if [[ -z `psql -Atqc '\list mydatabase' postgres` ]]; then createdb mydatabase; fi

Answer 4

psql -l|awk '{print $1}'|grep -w <database>

shorter version

Answer 5

For completeness, another version using regex rather than string cutting:

psql -l | grep '^ exact_dbname\b'

So for instance:

if psql -l | grep '^ mydatabase\b' > /dev/null ; then
  echo "Database exists already."
  exit
fi

Answer 6

I'm still pretty inexperienced with shell programming, so if this is really wrong for some reason, vote me down, but don't be too alarmed.

Building from kibibu's answer:

# If resulting string is not zero-length (not empty) then...
if [[ ! -z `psql -lqt | cut -d \| -f 1 | grep -w $DB_NAME` ]]; then
  echo "Database $DB_NAME exists."
else
  echo "No existing databases are named $DB_NAME."
fi