If the file .csoundrc exists, it will be used to set the command line parameters. These can be overridden. Csound 5.00 and newer versions read this file from the HOME directory first (or the full path file name defined by the CSOUNDRC environment variable), and then the current directory. If both exist, options in the .csoundrc in the current directory will have higher precedence. It uses the same form as a .csd file, but no tags are needed. Lines beginning with # or ; are treated as comments.
A .csoundrc file can contain something like this:
-+rtaudio=portaudio -odac2 -iadc2 -+rtmidi=winmme -M1 -Q1 -m0
In this case, csound will generate real-time output and take realtime input from device 2, using the portaudio driver interface. It will input and output realtime MIDI on interface 1. It will print very few messages (-m0). These options will be used by default when other options are not given inside the <CsOptions> of the .csd file or the command line (See Order of precendence).