Check if mysql database exists, perform action based on result

Question

Is it possible from within a bash script to check if a mysql database exists. Depending on the result then perform another action or terminate the script?

Answer 1

Also you can ask to use the database and then handle the exit code.

$ if mysql -uroot -pxxx -e "USE mysql"; then echo "exists"; fi
exists

$ if mysql -uroot -pxxx -e "USE doesnotexist"; then echo "exists"; fi
ERROR 1049 (42000) at line 1: Unknown database 'doesnotexist'

Or inspect $? after the call.

Answer 2

mysqlshow will not show underscore characters '_' in the database name.

mysqlshow $DOMAIN %

https://dev.mysql.com/doc/refman/5.1/en/mysqlshow.html

Answer 3

If it helps, I did this for MariaDB on Debian Stretch:

DB_CHECK=$(mysqlshow "${DB_NAME}" | grep "Unknown database") 1> /dev/null
if [ ! -z "${DB_CHECK}" ]; then
    echo "Database found."
else
    echo "Database not found."
fi

Short explanation: The result of mysqlshow for database name in variable $DB_NAME is checked for "Unknown database". If that string is found it's put into variable $DB_CHECK. Then finally the -z comparison checks if the $DB_CHECK variable is empty.

If $DB_CHECK is empty then "Unknown database" did not appear in the mysqlshow response. Probably not 100% reliable, like if the connection failed or whatever. (I've not tested that.)

Answer 4

Here is an alternate version:

 RESULT=`mysql -u$USER -p$PASSWORD -e "SHOW DATABASES" | grep $DATABASE`
 if [ "$RESULT" == "$DATABASE" ]; then
    echo "Database exist"
 else
    echo "Database does not exist"
 fi

IF there is a DB named abcd and we use -Fo after grep then for the search result of DB a/ab/abc the script will show the result Database exist.

Answer 5

Another solution without grep:

FOUND_DATABASES=`MYSQL_PWD="${DB_PASSWORD}" mysql \
 -u "${DB_PASSWORD}" \
 --skip-column-names \
 --batch \
 -e "SHOW DATABASES LIKE '${DB_NAME}'" | wc -l`

FOUND_DATABASES:

• 0 - there is no such database
• 1 - the database was found

Notes:

• MYSQL_PWD to disable the warning:

  mysql: [Warning] Using a password on the command line interface can be insecure.

• --skip-column-names to hide columns

• --batch to disable borders like +-----------+

Answer 6

Here's how i did it inside a bash script:

#!/bin/sh

DATABASE_USER=*****
DATABASE_PWD=*****
DATABASE_NAME=my_database

if mysql -u$DATABASE_USER -p$DATABASE_PWD -e "use $DATABASE_NAME";
then
echo "Database $DATABASE_NAME already exists. Exiting."
exit
else
echo Create database
mysql -u$DATABASE_USER -p$DATABASE_PWD -e "CREATE DATABASE $DATABASE_NAME"
fi