Environment variables

The GODEBUG environment variable controls specific runtime behaviors in Go programs by setting key=value pairs to opt into or out of compatibility changes. Set it as a comma-separated list before running your program to override defaults like HTTP/2 usage or panic behavior.

export GODEBUG=http2client=0,panicnil=1

You can also set defaults permanently in your go.mod file using the godebug block or in source files with //go:debug directives.

GODEBUG is a switchboard that lets you tell your Go program to behave like an older version or disable specific new features. It matters because it prevents your code from breaking when you upgrade Go, acting like a compatibility mode for your application.