After a lot of hair pull and experimentation on a real OSX machine I've discovered an insurmountable roadblock to doing this with poll() in OSX. From man poll:
Devices includes terminals, real and virtual.
select() might still support them. You can see code here on how to use select(). linux code, but should be applicable to OSX.
Quote:
This is really interesting however it print everything uppercase at the end, I want to do something interactive where the user type and the system print back uppercase
Well, that's how pipes work. They buffer until they're full. To use them in a nonblocking manner you'll need to set them nonblocking, I think:
...though this behavior may vary from system to system.
Using a seperate process and a pipe to convert lowercase to uppercase is overkill, but I bet you know that and this is just an example...
---------- Post updated at 12:41 AM ---------- Previous update was at 12:31 AM ----------
Quote:
Also I dont get why poll for p[1].
To make sure write(p[1].fd, data, size) doesn't block. Imagine that the child and the parent are writing at the same time, waiting for each other. They'll both wait forever. Instead, we write only when the pipe can hold it.
I have encountered a strange problem dealing with pipes
and forking. The program basicaly does this:
cat file | tbl | eqn | groff
Now, I have a parent process that forks children
that that exec the stuff that they should. The pipes defined
in the parent are the ones used.
The chain goes... (1 Reply)
I use read often in scripts to filter the right part into a variable like:
$ print "abc cde efg" | read k l ; print "k=$k, l=$l"
k=, l=
This works on linux and unix versions I work with. On OSX 10.4 this
doesn't work. I found a workaround but would like to know
why the original line... (5 Replies)
Basically I am trying to write a short script to report total space used on /u0? file systems. This is what I was trying to do:df -k /u0? | grep -v kbytes | awk '{ printf $2 "+" }' | sed s/.$// | bcBut it returns no output.
This works however: > A=`df -k /u0? |grep -v kbytes | awk '{ printf $2... (2 Replies)
Is there a way to know whether is pipe is opened in read or write mode.I mean is there any signal that is generated when a pipe is opened in read or write mode.
If you have some solution .please let me know ........ (2 Replies)
Hi,
Can any one please help me with this. Am struggling hard to get a solution.
I am doing telnet through a C program and getting the stdout file descriptor of the remote machine to pipe.
read() function is getting data, But whenl it receives SOH character ie. ^A ( Start of heading = Console... (2 Replies)
Could anyone tell me whats wrong whit this piping? the commands that they execute are correct. the command I am trying is ls|wc. Both processes go to the right if statement.
for(i=0;i<argc;i++){
if(i==0&&argc>1){//first command
if(pipe(pipa1)==-1)
... (2 Replies)
Hello !
I want to process a text file in order to extract desired data using sed and grep... Now I am facing a problem piping to grep... nothing happens..
The text consists of blocks of 3 lines that may (or not) contain the Desired data.
the desired data is on each 2... (4 Replies)
hi i am having issues with extra pipe.
i have a data file and i need to remove the extra pipe in the(example 4th and 7thline) in datafile. there are many other line and filed like this which i need to remove from files. The sample data is below:
270 31|455004|24/03/2010|0001235|72
271... (3 Replies)
Hi,guys:
I want to use c to implement a pipe. For example:
ps auxwww | grep fred | more
I forked three child processes. Each is responsible for each command, and pipe to next one.
for(i=0;i<2;i++)
pipe(fd)
if(child==1) // child 1
{
close(1)
dup2(fd,1)
close(fd)
}... (3 Replies)
Hi!
I'm having problems with pipes... I need comunnications with childs processes and parents, but only one child can comunnicate with parent (first child), others childs can't.
A brief of code:
if(pipe(client1r)<0){
perror("pipe");
}
... (1 Reply)
Discussion started by: serpens11
1 Replies
LEARN ABOUT LINUX
pcap_get_selectable_fd
PCAP_GET_SELECTABLE_FD(3PCAP)PCAP_GET_SELECTABLE_FD(3PCAP)NAME
pcap_get_selectable_fd - get a file descriptor on which a select() can be done for a live capture
SYNOPSIS
#include <pcap/pcap.h>
int pcap_get_selectable_fd(pcap_t *p);
DESCRIPTION
pcap_get_selectable_fd() returns, on UNIX, a file descriptor number for a file descriptor on which one can do a select() or poll() to wait
for it to be possible to read packets without blocking, if such a descriptor exists, or -1, if no such descriptor exists. Some network
devices opened with pcap_create() and pcap_activate(), or with pcap_open_live(), do not support select() or poll() (for example, regular
network devices on FreeBSD 4.3 and 4.4, and Endace DAG devices), so -1 is returned for those devices.
Note that in:
FreeBSD prior to FreeBSD 4.6;
NetBSD prior to NetBSD 3.0;
OpenBSD prior to OpenBSD 2.4;
Mac OS X prior to Mac OS X 10.7;
select() and poll() do not work correctly on BPF devices; pcap_get_selectable_fd() will return a file descriptor on most of those versions
(the exceptions being FreeBSD 4.3 and 4.4), but a simple select() or poll() will not indicate that the descriptor is readable until a full
buffer's worth of packets is received, even if the read timeout expires before then. To work around this, an application that uses
select() or poll() to wait for packets to arrive must put the pcap_t in non-blocking mode, and must arrange that the select() or poll()
have a timeout less than or equal to the read timeout, and must try to read packets after that timeout expires, regardless of whether
select() or poll() indicated that the file descriptor for the pcap_t is ready to be read or not. (That workaround will not work in FreeBSD
4.3 and later; however, in FreeBSD 4.6 and later, select() and poll() work correctly on BPF devices, so the workaround isn't necessary,
although it does no harm.)
Note also that poll() doesn't work on character special files, including BPF devices, in Mac OS X 10.4 and 10.5, so, while select() can be
used on the descriptor returned by pcap_get_selectable_fd(), poll() cannot be used on it those versions of Mac OS X. Kqueues also don't
work on that descriptor. poll(), but not kqueues, work on that descriptor in Mac OS X releases prior to 10.4; poll() and kqueues work on
that descriptor in Mac OS X 10.6 and later.
pcap_get_selectable_fd() is not available on Windows.
RETURN VALUE
A selectable file descriptor is returned if one exists; otherwise, -1 is returned.
SEE ALSO pcap(3PCAP), select(2), poll(2)
5 April 2008 PCAP_GET_SELECTABLE_FD(3PCAP)