change /etc/localtime to UTC time? I noticed it is common for programming languages to utilize /etc/localtime when determining the current time to display for a user. In particular, I know that Ruby relies on /etc/localtime if the "TZ" environment variable is not set. I am able to read the contents of this binary like so:

$ zdump /etc/localtime
/etc/localtime  Sun Aug 12 16:53:50 2018 EDT


It seems, therefore, the time used by programming languages is Eastern Time North America. It makes sense, I am in the East Coast of the US. However, how can I change this file to UTC so that the programming language and software on my computer uses UTC rather than EDT time?
You can set the time in System Preferences, and that time should be reflected back in /etc/localtime.

If you want to do it at the command line, use the systemsetup tool (which has to be run via sudo, fyi).

Here are the relevant commands from sudo systemsetup -help:

Usage: systemsetup -gettimezone
    Display current time zone.

Usage: systemsetup -settimezone &lt;timezone&gt;
    Set current time zone to &lt;timezone&gt;. Use "-listtimezones" to list time zones.

Usage: systemsetup -listtimezones
    List time zones supported by this machine.