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Top Forums Programming how could i make a program mixed with many "|", "<" and ">" Post 302072050 by strugglingman on Wednesday 26th of April 2006 07:15:15 PM
Old 04-26-2006
Data how could i make a program mixed with many "|", "<" and ">"

I have written following code to do: ls -l | wc -w, it works:
but when there are not only a single "|", if there are more such as:
ls -l | sort -r | sort | sort -r, This program does not work, i want to know how could i deal with it when there are more "|", another situation is that, if it mixes "|" and "<" or ">", such as: cat < apa | wc | wc >h***, this is also complex, how could i deal with these? thank you very much

(The following is just for a single "|")
void pipeProcess(char *args1[], char *args2[]) {
int thepipe[2], pid;

if(pipe(thepipe) == -1)
oops("Can not get a pipe", 1);
/* Create a new process */
if((pid = fork()) == -1)
oops("Can not fork", 2);

if(pid >0) {/* This is parent process */
close(thepipe[1]); /* parent does not write to pipe */
if(dup2(thepipe[0], 0) == -1) /* let parent read interface attaches to stdin */
oops("Could not redirect stdin", 3);
close(thepipe[0]); /* close thepipe[0] interface because it has attached to stdin */
execvp(args2[0], args2);
oops(*args2, 4);
}

/* Child process executes av[1] and writesinto pipe */
close(thepipe[0]); /* Child does not read from pipe */
if(dup2(thepipe[1], 1) == -1)
oops("Could not redirect stdout", 4);
close(thepipe[1]);
execvp(args1[0], args1);
oops(*args1, 5);
}
 

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filter_create_fd(3)						   util/filter.h					       filter_create_fd(3)

NAME
filter_create_fd - Create a sub process and return the requested pipes SYNOPSIS
#include <util/filter.h> NEOERR *filter_create_fd(const char *cmd, int *fdin, int *fdout, int *fderr, pid_t *pid); ARGUMENTS
cmd -> the sub command to execute. Will be executed with /bin/sh -c fdin -> pointer to return the stdin pipe, or NULL if you don't want the stdin pipe fdout -> pointer to return the stdout pipe, or NULL if you don't want the stdout pipe fderr -> pointer to return the stderr pipe, or NULL if you don't want the stderr pipe DESCRIPTION
filter_create_fd and filter_create_fp are what popen been: a mechanism to create sub processes and have pipes to all their input/output. The concept was taken from mutt, though python has something similar with popen3/popen4. You control which pipes the function returns by the fdin/fdout/fderr arguments. A NULL value means "don't create a pipe", a pointer to an int will cause the pipes to be created and the value of the file descriptor stored in the int. You will have to close(2) the file descriptors yourself. RETURN VALUE
fdin -> the stdin file descriptor of the sub process fdout -> the stdout file descriptor of the sub process fderr -> the stderr file descriptor of the sub process pid -> the pid of the sub process SEE ALSO
filter_wait(3), filter_create_fp(3), filter_create_fd ClearSilver 12 July 2007 filter_create_fd(3)
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