using variables with postgres

Does postgres support the use of variables as in the example below?

update table1 set column1=(at)variable
where column2='text4column2'
and @variable=(select column3 from table2 where column4='text4column4');

If not, how do I execute a statement like this in postgres?

Please respond as soon as possible as I am working on a time sensitive
project that depends on this.
Thank you and have a great day