Using an environment variable in a PSQL script

Question

Is it possible to use a Linux environment variable inside a .sql file? I'm using the copy/select query to write to an output file, and I'll like to put that directory in a variable. So I want to do something like:

COPY (SELECT * FROM a) TO $outputdir/a.csv 

Outputdir would be set in my environment. Is this possible?

Answer 1

You can store the result of a shell command inside a psql variable like this:

\set afile `echo "$outputdir/a.csv"` COPY (SELECT * FROM a) TO :'afile'; 

Another (better in my opinion) solution is to use only psql variables, see this answer of mine about psql variables, which is similar to your example. A example for your case would be:

\set outputdir '/path/to/output' \set afile :outputdir '/a.csv' COPY (SELECT * FROM a) TO :'afile'; 

Note that, in the example, you need to set the variable inside the script file, but you can skip the first line if you set it when you call psql:

psql --set=outputdir="$outputdir" <conn parameters> -f /path/to/yourscript.sql