[SOLVED] Difference bw ctrl C & ctrl D & ctrl Z

[Lakshmipathi]

I have a command running like:

tail -f logfile.txt

That's the difference between using
ctrl+c or
ctrl+z or
ctrl+d

ctrl+c seems like will terminate the program.
but with ctrl+z is suspended ?
what's this ctrl+d will do ?

[gerard4143]

You can use control d for EOF(end of file)

[Lakshmipathi]

Thanks gerard4143
So finally
Ctrl + C To terminate
Ctrl + D signals EOF
Ctrl + Z suppends a program

HTH someone.

[Cabhan]

Just to clarify a bit: what Ctrl-C actually does is send a SIGQUIT signal to the process. A process is able to intercept this signal and do whatever it likes: for instance, from your Bash prompt, try hitting Ctrl-C. In Bash, it just cancels whatever you've typed and gives you a blank prompt (as opposed to quitting Bash).

[wje_lf]

Here it goes: I'm posting too much information, I'm sure.

[W]hat Ctrl-C actually does is send a SIGQUIT signal to the process.

Actually, the signal usually associated with the ^C character is not SIGQUIT, but SIGINT.

With that slight modification, what Cabhan says is true in normal circumstances. And this is definitely true:

A process is able to intercept this signal and do whatever it likes

But there are more ways in which a running program can do whatever it likes.

First, it can associate with each of certain signals any ASCII character it likes. In addition, it is customary to specify the character hex FF to mean "Don't let any key on the keyboard cause this signal to be sent." Then your program doesn't have to go out of its way to explicitly ignore that signal or catch it.

Here are some signals, and the characters usually associated with them (which are overridable by the running program):

SIGINT   ^C   (default action: terminate the process)
SIGQUIT  ^\   (default action: terminate the process and dump to a core file)
SIGSUSP  ^Z   (default action: suspend the process)

As Cabhan says, for each of these signals, a running program can either accept the default action, ignore the signal, or specify some other action written in the program's code.

Beyond signals, the running program can also specify which character (if any) is the end of file character. The default character for this, as gerard4143 and Lakshmipathi say, is ^D.

The interested C programmer would do well to type this at the shell prompt:

man tcsetattr

[Cabhan]

Right, so I thought it was SIGINT, but I wasn't sure, and I checked signal(7), and saw SIGQUIT as "Interrupt from keyboard".

I have now rechecked that, and have seen that I was reading the wrong line <_<;.

[wje_lf]

I was reading the wrong line

That's ok. I never make mistakes. (cough cough CHOKE)

[Lakshmipathi]

Thanks guyz - For providing more insight to this topic

[drl]

Hi.

I like the way Stevens wrote in these topics:

The handling of terminal I/O is a messy area, regardless of the operating system. (Terminal I/O, Chapter 11)

Signals are software interrupts.
(Signals, Chapter 10)

If you are interested enough to explore farther, see the book below ... cheers, drl

Title: Advanced Programming in the UNIX(R) Environment
Author: W. Richard Stevens
Edition: 1st
Date: 1992
Publisher: Addison-Wesley Professional
ISBN: 0-201-56317-7
Pages: 768
Categories:  unix, system calls, programming, coding
Comments: 4.5 stars at Amazon; there is a second edition 2005

[wje_lf]

I agree. Advanced Programming in the UNIX Environment rocks, as do W. Richard Stevens's books on network programming.