66 lines
1.4 KiB
C
66 lines
1.4 KiB
C
/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/*
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* This simple program illustrates output redirection via dup(2).
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*
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* Compare:
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* ./a.out
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* ./a.out >/dev/null
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* ./a.out 2>/dev/null
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#define STDOUT_MSG "A message to stdout.\n"
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#define STDERR_MSG "A message to stderr.\n"
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void
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writeBoth(const char *mark) {
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int len, marklen;
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marklen = strlen(mark);
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if (write(STDOUT_FILENO, mark, marklen) != marklen) {
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perror("unable to write marker to stdout");
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exit(EXIT_FAILURE);
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}
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len = strlen(STDOUT_MSG);
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if (write(STDOUT_FILENO, STDOUT_MSG, len) != len) {
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perror("unable to write to stdout");
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exit(EXIT_FAILURE);
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}
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if (write(STDERR_FILENO, STDERR_MSG, len) != len) {
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perror("unable to write to stdout");
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exit(EXIT_FAILURE);
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}
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}
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int
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main() {
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writeBoth("before dup2\n");
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if (dup2(STDOUT_FILENO, STDERR_FILENO) < 0) {
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perror("Unable to redirect stderr to stdout");
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exit(EXIT_FAILURE);
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}
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writeBoth("after dup2\n");
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}
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