You need to query postgresql and use the result in a bash script
You can use the psql command to do the job and let it write the result on the screen. e.g.
psql -d testdb -c "select * from testtable"
This will deliver the result on the screen. To pipe it into a file you use:
psql -d testdb -c "select * from testtable" -o /tmp/testresult.txt
You can read the file in your bash script.
About the Author
Wim Peeters is electronics engineer with an additional master in IT and over 30 years of experience including time spent in support, development, consulting, training and database administration. Wim has worked with SQL Server since version 6.5. He has developed in C/C++, Java and C# on Windows and Linux in different European countries and different European languages. He writes knowledge base articles to solve IT problems and publishes them on the Lubby Knowledge Platform where he is one of the most important contributors and the main developer.