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#include "apue.h"
#include <sys/wait.h>
#define DEF_PAGER "/bin/more" /* default pager program */
int
main(int argc, char *argv[])
{
int n;
int fd[2];
pid_t pid;
char *pager, *argv0;
char line[MAXLINE];
FILE *fp;
if (argc != 2)
err_quit("usage: a.out <pathname>");
if ((fp = fopen(argv[1], "r")) == NULL)
err_sys("can't open %s", argv[1]);
if (pipe(fd) < 0)
err_sys("pipe error");
if ((pid = fork()) < 0) {
err_sys("fork error");
} else if (pid > 0) { /* parent */
close(fd[0]); /* close read end */
/* parent copies argv[1] to pipe */
while (fgets(line, MAXLINE, fp) != NULL) {
n = strlen(line);
if (write(fd[1], line, n) != n)
err_sys("write error to pipe");
}
if (ferror(fp))
err_sys("fgets error");
close(fd[1]); /* close write end of pipe for reader */
if (waitpid(pid, NULL, 0) < 0)
err_sys("waitpid error");
exit(0);
} else { /* child */
close(fd[1]); /* close write end */
if (fd[0] != STDIN_FILENO) {
if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)
err_sys("dup2 error to stdin");
close(fd[0]); /* don't need this after dup2 */
}
/* get arguments for execl() */
if ((pager = getenv("PAGER")) == NULL)
pager = DEF_PAGER;
if ((argv0 = strrchr(pager, '/')) != NULL)
argv0++; /* step past rightmost slash */
else
argv0 = pager; /* no slash in pager */
if (execl(pager, argv0, (char *)0) < 0)
err_sys("execl error for %s", pager);
}
exit(0);
}
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