Like a lot of systems folks I use sed, a lot. It is probably an unhealthy amount of sed use but so be it. I operate on a lot of Linux servers but my desktop environment of choice is Mac OS X which means BSD tools (not the Linux-y GNU tools).
The differences are relatively subtle between BSD sed and GNU sed. However, most of my work is done through iTerm (a literal black box)....
Disabling Mac OS X El Capitan System Integrity Protection
Apple has introduced a new security feature in Mac OS X El Capitan (10.11) called System Integrity Protection (sometimes referred to as rootless).
What is System Integrity Protection? According to Apple’s documentation:
A new security policy that applies to every running process, including privileged code and code that runs out of the sandbox. The policy extends additional protections to components on disk and at run-time, only allowing system binaries to be modified by the system installer and software updates....