80 lines
1.7 KiB
C
80 lines
1.7 KiB
C
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/* 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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/* This is basically the same as 'pipe2.c', but using
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* popen(3). Make sure to illustrate the dangers of
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* invoking a shell on user-provided input.
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*
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* $ env PAGER="more; touch /tmp/boo" ./a.out popen.c
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* $ env PAGER="more; rm /etc/passwd 2>/dev/null"
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* ./a.out popen.c
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*/
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#include <sys/wait.h>
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#include <err.h>
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#include <errno.h>
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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 DEF_PAGER "/usr/bin/more"
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int
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main(int argc, char **argv) {
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FILE *pipe;
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char line[BUFSIZ], *pager;
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FILE *fp;
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if (argc != 2) {
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(void)fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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if ((pager = getenv("PAGER")) == NULL)
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pager = DEF_PAGER;
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if ((pipe = popen(pager, "w")) == NULL) {
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(void)fprintf(stderr,"Unable to open pipe to %s: %s\n",
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pager, strerror(errno));
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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if ((fp = fopen(argv[1], "r")) == NULL) {
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(void)fprintf(stderr, "can't open %s\n", argv[1]);
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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while (fgets(line, BUFSIZ, fp) != NULL) {
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(void)fprintf(pipe, "==> %s", line);
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}
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if (ferror(fp)) {
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err(EXIT_FAILURE, "fgets");
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/* NOTREACHED */
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}
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if (pclose(pipe) == -1) {
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err(EXIT_FAILURE, "pclose");
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/* NOTREACHED */
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}
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return EXIT_SUCCESS;
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}
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