FreeCalypso > hg > fc-rfcal-tools

annotate scripts/fc-rfcal-tee.c @ 98:615df2fb1ec3

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doc/Tx-cal-theory: update with both theory and practice
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 17 Jul 2017 22:49:35 +0000
parents 713749548df6
children
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713749548df6 fc-rfcal-tri900 script and fc-rfcal-tee helper implemented
Mychaela Falconia <falcon@freecalypso.org>
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1 /*
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2 * This C program is a workaround for a stupidity in Bourne shell.
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3 * I would like to have a shell script like the following:
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4 *
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5 * set -e
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6 * fc-rfcal-vcxo | tee vcxo
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7 * fc-rfcal-rxband 900 | tee rx-900
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8 * fc-rfcal-rxband 1800 | tee rx-1800
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9 * ...
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10 *
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11 * and if one of the fc-rfcal-* steps encounters an error and returns
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12 * a non-zero exit code, I want the script to stop right there, hence
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13 * the set -e at the beginning. Sounds like a very simple and reasonable
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14 * desire, doesn't it? But oh noes - because I am piping the output
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15 * through tee in order to save it in log files, the process return
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16 * codes from fc-rfcal-* get *ignored* by the shell (the always successful
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17 * exit code from tee is all that counts), and it will keep executing
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18 * the following lines without stopping.
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19 *
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20 * This C program is like tee, but with invokation of the "main" command
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21 * whose output is to be saved built in. The process forks, the "main"
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22 * command is executed in the child, the parent performs the tee function,
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23 * and when the child terminates, the parent propagates its exit code.
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24 */
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25
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26 #include <sys/types.h>
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27 #include <sys/file.h>
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28 #include <sys/wait.h>
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29 #include <stdio.h>
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30 #include <stdlib.h>
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31 #include <unistd.h>
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32
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33 char shell_pathname[] = "/bin/sh";
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34 int log_fd;
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35
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36 tee_process(pipe_fd)
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37 {
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38 char buf[1024];
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39 int cc;
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40
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41 while ((cc = read(pipe_fd, buf, sizeof buf)) > 0) {
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42 write(1, buf, cc);
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43 if (log_fd > 2)
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44 write(log_fd, buf, cc);
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45 }
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46 }
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47
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48 main(argc, argv)
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49 char **argv;
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50 {
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51 int p[2];
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52 pid_t child, waitres;
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53 int status;
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54
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55 if (argc != 3) {
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56 fprintf(stderr, "usage: %s command logfile\n", argv[0]);
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57 exit(1);
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58 }
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59 if (pipe(p) < 0) {
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60 perror("pipe");
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61 exit(1);
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62 }
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63 child = fork();
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64 if (child < 0) {
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65 perror("fork");
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66 exit(1);
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67 }
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68 if (!child) {
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69 dup2(p[1], 1);
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70 close(p[0]);
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71 close(p[1]);
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72 execl(shell_pathname, "sh", "-c", argv[1], 0);
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73 perror(shell_pathname);
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74 exit(1);
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75 }
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76 close(p[1]);
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77 log_fd = open(argv[2], O_WRONLY|O_CREAT|O_TRUNC, 0666);
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78 if (log_fd < 0)
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79 perror(argv[2]);
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80 tee_process(p[0]);
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81 waitres = waitpid(child, &status, 0);
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82 if (waitres == child && WIFEXITED(status))
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83 exit(WEXITSTATUS(status));
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84 else
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85 exit(1);
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86 }