i3-migrate-config-to-v4 - migrates your i3 config file
mv ~/.i3/config ~/.i3/old.config
i3-migrate-config-to-v4 ~/.i3/old.config > ~/.i3/config
i3-migrate-config-to-v4 is a Perl script which migrates your old (< version
4) configuration files to a version 4 config file. The most significant
changes are the new commands (see the release notes).
This script will automatically be run by i3 when it detects an old
config file. Please migrate your config file as soon as possible. We plan to
include this script in all i3 release until 2012-08-01. Afterwards, old
config files will no longer be supported.
Michael Stapelberg and contributors