I am trying to create a pipe that will direct stdout to in side of the pipe, and stdin to the out side of the pipe - I created two child processes to handle this. However, my pipe doesn't seem to be working correctly. Did I use execv() correctly? Command1[] and command2[] represent the two commands in the pipe statement that is written in a cissh shell (e.g. "ls -C | sort -r). So I want cisshPipe.c to direct stdout to the in side of the pipe and direct stdin to the out side of the pipe so that the command "ls -C | sort -r" would print a sorted list in reverse order of the files in the cissh directory. Below is my code for the pipe function. I'd greatly appreciate help from someone.Thanks!
Code:
/* cisshPipe.c
*/
/* External functions --
*/
extern void error(char* message);
//extern wait(int*status);
/* cisshPipe(char* command1[], char* command2[])
* handles command lines with pipes.
*/
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
void
cisshPipe(char* command1[], char* command2[])
{
pid_t pid;
pid_t pid1;
int status;
int commpipe[2]; /* This holds the input and output of the pipe */
if(pipe(commpipe)){ /* Setup communication pipeline */
fprintf(stderr,"Pipe error\n");
exit(1);
}
if ( (pid = fork()) == -1 ){
fprintf(stderr,"Fork error. Exiting.\n"); /* something went wrong with forking */
}
if (pid ==0) {
// first child process
close(commpipe[1]);
dup2(commpipe[0],1); /* Replace in side of pipe with stdout */
close(commpipe[0]);
execv(command1[0], command1);
if ( (pid1 = fork()) == -1 ){
fprintf(stderr,"Fork error. Exiting.\n"); /* something went wrong with forking */
}
if(pid1 == 0){
/* second child process */
close(commpipe[0]);
dup2(commpipe[1],0); /* Replace out side of pipe with stdin */
close(commpipe[1]);
execv(command2[0], command2);
}
else {
close(commpipe[1]);
close(commpipe[0]);
if(wait(&status) < 0)
{
error("cissh: error waiting for child.");
perror("wait");
}
}
}
else {
close(commpipe[1]);
close(commpipe[0]);
if(wait(&status) < 0)
{
error("cissh: error waiting for child.");
perror("wait");
}
}
}
Last edited by jre247; 04-28-2010 at 10:19 AM..
Reason: Please use code tags!
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Discussion started by: ymc1g11
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LEARN ABOUT PLAN9
pipe
PIPE(2) System Calls Manual PIPE(2)NAME
pipe - create an interprocess channel
SYNOPSIS
#include <u.h>
#include <libc.h>
int pipe(int fd[2])
DESCRIPTION
Pipe creates a buffered channel for interprocess I/O communication. Two file descriptors are returned in fd. Data written to fd[1] is
available for reading from fd[0] and data written to fd[0] is available for reading from fd[1].
After the pipe has been established, cooperating processes created by subsequent fork(2) calls may pass data through the pipe with read and
write calls. The bytes placed on a pipe by one write are contiguous even if many processes are writing. Write boundaries are preserved:
each read terminates when the read buffer is full or after reading the last byte of a write, whichever comes first.
The number of bytes available to a read(2) is reported in the Length field returned by fstat or dirfstat on a pipe (see stat(2)).
When all the data has been read from a pipe and the writer has closed the pipe or exited,read(2) will return 0 bytes. Writes to a pipe with no reader will generate a note sys: write on closed pipe.
SOURCE
/sys/src/libc/9syscall
SEE ALSO intro(2), read(2), pipe(3)DIAGNOSTICS
Sets errstr.
BUGS
If a read or a write of a pipe is interrupted, some unknown number of bytes may have been transferred.
When a read from a pipe returns 0 bytes, it usually means end of file but is indistinguishable from reading the result of an explicit write
of zero bytes.
PIPE(2)