Signal EOF in mac osx terminal

If you want to see what EOF is set as in your terminal, you can type

stty all

on my mac, this gives the output -

speed 9600 baud; 24 rows; 80 columns;
lflags: icanon isig iexten echo echoe -echok echoke -echonl echoctl
    -echoprt -altwerase -noflsh -tostop -flusho pendin -nokerninfo
-extproc
iflags: -istrip icrnl -inlcr -igncr ixon -ixoff ixany imaxbel iutf8
-ignbrk brkint -inpck -ignpar -parmrk
oflags: opost onlcr -oxtabs -onocr -onlret
cflags: cread cs8 -parenb -parodd hupcl -clocal -cstopb -crtscts -dsrflow
-dtrflow -mdmbuf
discard dsusp   eof     eol     eol2    erase   intr    kill    lnext   
^O      ^Y      ^D      <undef> <undef> ^?      ^C      ^U      ^V      
min     quit    reprint start   status  stop    susp    time    werase  
 1       ^\      ^R      ^Q      ^T      ^S      ^Z      0       ^W     

You can see four lines up from the bottom, three cells in eof is ^D.

There's a fuller description here which is where I found the information.

By default, macOS (formerly OS X and Mac OS X) software recognizes EOF when Control-D is pressed at the beginning of a line. (I believe this behavior is similar for other versions of Unix as well.)

In detail, the actual operation is that, when Control-D is pressed, all bytes in the terminal’s input buffer are sent to the attached/foreground process using the terminal. At the start of a line, no bytes are in the buffer, so the process is told there are zero bytes available, and this acts as an EOF indicator.

This procedure doubles as a method of delivering input to the process before the end of a line: The user may type some characters and press Control-D, and the characters will be sent to the process immediately, without the usual wait for enter/return to be pressed. After this “send all buffered bytes immediately” operation is performed, no bytes are left in the buffer. So, when Control-D is pressed a second time, it is the same as the beginning of a line (no bytes are sent, and the process is given zero bytes), and it acts like an EOF.

You can learn more about terminal behavior by using the command “man 4 tty” in Terminal. The default line discipline is termios. You can learn more about the termios line discipline by using the command man termios.