How to find the mysql data directory from command line

You can issue the following query from the command line:

mysql -uUSER -p -e 'SHOW VARIABLES WHERE Variable_Name LIKE "%dir"'

Output (on Linux):

+---------------------------+----------------------------+
| Variable_name             | Value                      |
+---------------------------+----------------------------+
| basedir                   | /usr                       |
| character_sets_dir        | /usr/share/mysql/charsets/ |
| datadir                   | /var/lib/mysql/            |
| innodb_data_home_dir      |                            |
| innodb_log_group_home_dir | ./                         |
| lc_messages_dir           | /usr/share/mysql/          |
| plugin_dir                | /usr/lib/mysql/plugin/     |
| slave_load_tmpdir         | /tmp                       |
| tmpdir                    | /tmp                       |
+---------------------------+----------------------------+

Or if you want only the data dir use:

mysql -uUSER -p -e 'SHOW VARIABLES WHERE Variable_Name = "datadir"'