Honestly I had no idea what ctrl+d even did, I just knew it was a convenient way for me to close all the REPL programs I use. The fact that it is similar to pressing enter really surprised me, so I wanted to share this knowledge with you :)
Honestly I had no idea what ctrl+d even did, I just knew it was a convenient way for me to close all the REPL programs I use. The fact that it is similar to pressing enter really surprised me, so I wanted to share this knowledge with you :)
Ctl-D is the End-of-File character. Programs interpret it as “that’s it, the input you were reading has finished”, and react accordingly.
$ cat You sound very nice :) You sound very nice :) Bye<ctl-d>Bye Oh wait, and cool too Oh wait, and cool too <ctl-d> $The Ctl-D didn’t end the file when i typed “Bye” :( it only worked when I pressed Ctl-D on its own line. So how does cat know that it should ignore the EOF character if there is some text that comes before it?
What Ctl-D does is flush the input to the program, and the program sees how big that input is. If the length of the input is 0 that is interpreted as EOF. So Ctl-D is like Enter because they both flush the input, but Ctl-D is unlike Enter because it does not append a newline before flushing, and as a consequence you can send empty input (aka an EOF “character”) with Ctl-D.
When running cat this way, you are in “cooked mode”. A ctrl-d does nothing on a non-empty line.
The shell usually runs in non-cokked, or raw, mode as well as nonblocking mode. Where it sees (nearly) every key you press as you press them. Which is why it " sees" the ctrl-d even when you are not on an empty line.
You can learn more here:
This!
It’s merely a buffer flush, in case it’s empty, the program handling the input can choose how to interpret,
catdecides to do it as an EOF.Reason why it also works as exit.