Linux Application Development

Michael K. Johnson Erik W. Troan

cat.c

/* cat.c -- simple version of cat */
#include <stdio.h>
#include <unistd.h>

/* While there is data on standard in (fd 0), copy it to standard
   out (fd 1). Exit once no more data is available. */

int main(void) {
    char buf[1024];
    int len;
    
    /* len will be >= 0 while data is available, and read() is
       successful */
    while ((len = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
        if (write(1, buf, len) != len) {
            perror("write");
            return 1;
        }
    }

    /* len was <= 0; If len = 0, no more data is available. 
       Otherwise, an error occurred. */
    if (len < 0) {
        perror("read");
        return 1;
    }

    return 0;
}