title: How does the libc function isatty() work?
body: <p>I searched the linux repo and couldn't find a definition for it, so I guess it's something that comes with C or something like that? I'm trying to understand how <code>isatty</code> is able to tell whether a file descriptor is a terminal or not, and what it even means to "be a terminal," in technical language.</p>
  
  <p>I'm not really sure where to find its implementation, and if it's in assembly I won't really be able to follow along with it very easily.</p>