Im not sure I understand Chef conditional execution. I’d like to do some conditional

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Editorial Team

Asked: June 7, 20262026-06-07T02:44:54+00:00 2026-06-07T02:44:54+00:00

Im not sure I understand Chef conditional execution.

I’d like to do some conditional execution based on whether or not a database exists in Postgresql

So here’s my example

execute "add_db" do
  cwd "/tmp"
  user "dbuser"
  command "createdb -T template_postgis mydb"
  not_if 'psql --list|grep mydb'
end

Running psql --list|grep mydb return what you would expect if the db exists (the line with the dbname entry) and nothing at all if it doesnt.

So how does not_if only evaluate that? True or false? 1 or 0? Dont all processes return 0 if they are successful?

Anywho any advice would be greatly appreciated!

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Editorial Team · Answer 1 · 2026-06-07T02:44:56+00:00

Editorial Team

I just ran into this issue. My problem was that the not_if command was being run as ‘root’, not ‘dbuser’. If you change it to

not_if 'psql --list|grep mydb', :user => 'dbuser'

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