UPDATE with multiple WHERE conditions

I have a table with 3492 rows. I want to update a boolean column from
'false' to 'true' for 295 rows based on the value of another column.

Is there a way to access a file with those condition values? If not, should
I create a temporary table with one column containing those values, or do I
write a psql script with 295 lines, one for each row to be updated?

TIA,

Rich