How to send the output of a PostgreSQL query to a CSV file using the CLI (Command Line Interface)

Log into the PostgreSQL interface on the command line, you should see a similar screen like the one below

Welcome to psql 8.1.21, the PostgreSQL interactive terminal.
 
Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit
 
database=#

Type the following command
```
\o /tmp/output.csv
```
- Make sure the Postgres user has write privileges to the directory specified
- /tmp/output.csv is the directory and the csv file name
- \o = Put all query output into file output.csv
Run your sql query eg.
```
SELECT * FROM users;
```
Type \q to quit the PostgresSQL interface
Browse to the /tmp/ directory
Open the output.csv file and all the data from the users table will be within this CSV file, and the columns will be comma seperated.