How to send a simple string between two programs using pipes?

A regular pipe can only connect two related processes. It is created by a process and will vanish when the last process closes it.

A named pipe, also called a FIFO for its behavior, can be used to connect two unrelated processes and exists independently of the processes; meaning it can exist even if no one is using it. A FIFO is created using the mkfifo() library function.

Example

writer.c

#include <fcntl.h>#include <sys/stat.h>#include <sys/types.h>#include <unistd.h>int main(){    int fd;    char * myfifo = "/tmp/myfifo";    /* create the FIFO (named pipe) */    mkfifo(myfifo, 0666);    /* write "Hi" to the FIFO */    fd = open(myfifo, O_WRONLY);    write(fd, "Hi", sizeof("Hi"));    close(fd);    /* remove the FIFO */    unlink(myfifo);    return 0;}

reader.c

#include <fcntl.h>#include <stdio.h>#include <sys/stat.h>#include <unistd.h>#define MAX_BUF 1024int main(){    int fd;    char * myfifo = "/tmp/myfifo";    char buf[MAX_BUF];    /* open, read, and display the message from the FIFO */    fd = open(myfifo, O_RDONLY);    read(fd, buf, MAX_BUF);    printf("Received: %s\n", buf);    close(fd);    return 0;}

_{Note: Error checking was omitted from the above code for simplicity.}

From Creating Pipes in C, this shows you how to fork a program to use a pipe. If you don't want to fork(), you can use named pipes.

In addition, you can get the effect of prog1 | prog2 by sending output of prog1 to stdout and reading from stdin in prog2. You can also read stdin by opening a file named /dev/stdin (but not sure of the portability of that).

/***************************************************************************** Excerpt from "Linux Programmer's Guide - Chapter 6" (C)opyright 1994-1995, Scott Burkett *****************************************************************************  MODULE: pipe.c *****************************************************************************/#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <sys/types.h>int main(void){        int     fd[2], nbytes;        pid_t   childpid;        char    string[] = "Hello, world!\n";        char    readbuffer[80];        pipe(fd);        if((childpid = fork()) == -1)        {                perror("fork");                exit(1);        }        if(childpid == 0)        {                /* Child process closes up input side of pipe */                close(fd[0]);                /* Send "string" through the output side of pipe */                write(fd[1], string, (strlen(string)+1));                exit(0);        }        else        {                /* Parent process closes up output side of pipe */                close(fd[1]);                /* Read in a string from the pipe */                nbytes = read(fd[0], readbuffer, sizeof(readbuffer));                printf("Received string: %s", readbuffer);        }        return(0);}

dup2( STDIN_FILENO, newfd )

And read:

char reading[ 1025 ];int fdin = 0, r_control;if( dup2( STDIN_FILENO, fdin ) < 0 ){    perror( "dup2(  )" );    exit( errno );}memset( reading, '\0', 1025 );while( ( r_control = read( fdin, reading, 1024 ) ) > 0 ){    printf( "<%s>", reading );    memset( reading, '\0', 1025 );}if( r_control < 0 )    perror( "read(  )" );    close( fdin );    

But, I think that fcntl can be a better solution

echo "salut" | code