12-01-2011
C Program to search and read all named pipes in current directory
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
Write a C program to search the current directory for all pipes.
1. It will print the pipe names, one per line.
2. Print the number of pipes found.
3. Search for all pipes whose contents contain your ID and print the entire contents of that/those pipe(s).
2. Relevant commands, code, scripts, algorithms:
Running inside a bash shell, compiling with g++, professor provides a directory of pre-existing pipes and pipe writers to prevent the block that you get from waiting for a pipe read or write to start
3. The attempts at a solution (include all code and scripts):
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main()
{
FILE *read_fp;
char buffer[BUFSIZ + 1];
int chars_read;
memset(buffer, '\0', sizeof(buffer));
read_fp = popen("uname -a", "r");
if (read_fp != NULL) {
chars_read = fread(buffer, sizeof(char), BUFSIZ, read_fp);
if (chars_read > 0) {
printf("Output was:-\n%s\n", buffer);
}
pclose(read_fp);
exit(EXIT_SUCCESS);
}
exit(EXIT_FAILURE);
}
4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):
University of North Texas, Denton, Texas, USA
Course is 3600, "Systems" taught by Professor Goodman
www . cse . unt . edu /~goodman/CS3600/cs3600.html
Note: Without school/professor/course information, you will be banned if you post here! You must complete the entire template (not just parts of it).
I don't have a problem reading from the pipe. I can specify a named pipe with the popen command and read from a named pipe. The above code can do that. The problem I have is that I am given the task to read from all the named pipes in the directory using a C program. I can easily write a bash script like "for all files in *" do blah. I know that I can do a system call and I can make a system call for the pwd to figure some things out but I don't know how to isolate pipes from the general files inside the C program. In a bash script I can use "test" to do that but is there a way to suck a list of named pipes into a C program in Unix? Finding named pipe assistance seems to be quite difficult on google so I'm trying out here.
Any ideas how to pull in the list of pipes into the C program?
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PIPE(2) System Calls Manual PIPE(2)
NAME
pipe - create an interprocess communication channel
SYNOPSIS
#include <unistd.h>
int pipe(int fildes[2])
DESCRIPTION
The pipe system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in read and write operations. When
the pipe is written using the descriptor fildes[1] up to PIPE_MAX bytes of data are buffered before the writing process is suspended. A
read using the descriptor fildes[0] will pick up the data.
PIPE_MAX equals 7168 under Minix, but note that most systems use 4096.
It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent fork calls) will pass data
through the pipe with read and write calls.
The shell has a syntax to set up a linear array of processes connected by pipes.
Read calls on an empty pipe (no buffered data) with only one end (all write file descriptors closed) returns an end-of-file.
The signal SIGPIPE is generated if a write on a pipe with only one end is attempted.
RETURN VALUE
The function value zero is returned if the pipe was created; -1 if an error occurred.
ERRORS
The pipe call will fail if:
[EMFILE] Too many descriptors are active.
[ENFILE] The system file table is full.
[ENOSPC] The pipe file system (usually the root file system) has no free inodes.
[EFAULT] The fildes buffer is in an invalid area of the process's address space.
SEE ALSO
sh(1), read(2), write(2), fork(2).
NOTES
Writes may return ENOSPC errors if no pipe data can be buffered, because the pipe file system is full.
BUGS
Should more than PIPE_MAX bytes be necessary in any pipe among a loop of processes, deadlock will occur.
4th Berkeley Distribution August 26, 1985 PIPE(2)