Give fish_test_helper slightly better argument parsing and help

src/fish_test_helper.cpp

@@ -4,6 +4,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 
+#include <algorithm>
 #include <csignal>
 #include <cstdio>
 #include <cstdlib>
@@ -34,7 +35,7 @@ static void report_foreground() {
 }
 
 static void sigint_parent() {
-    // SIGINT the parent after 1 second, then exit
+    // SIGINT the parent after a time, then exit
     int parent = getppid();
     usleep(1000000 / 4);  //.25 secs
     kill(parent, SIGINT);
@@ -67,26 +68,67 @@ static void print_fds() {
     fputc('\n', stdout);
 }
 
+static void show_help();
+
+/// A thing that fish_test_helper can do.
+struct fth_command_t {
+    /// The argument to match against.
+    const char *arg;
+
+    /// Function to invoke.
+    void (*func)();
+
+    /// Description of what this does.
+    const char *desc;
+};
+
+static fth_command_t s_commands[] = {
+    {"become_foreground_then_print_stderr", become_foreground_then_print_stderr,
+     "Claim the terminal (tcsetpgrp) and then print to stderr"},
+    {"report_foreground", report_foreground,
+     "Continually report to stderr whether we own the terminal"},
+    {"sigint_parent", sigint_parent, "Wait .25 seconds, then SIGINT the parent process"},
+    {"print_stdout_stderr", print_stdout_stderr, "Print 'stdout' to stdout and 'stderr' to stderr"},
+    {"print_pid_then_sleep", print_pid_then_sleep, "Print our pid, then sleep for .5 seconds"},
+    {"print_pgrp", print_pgrp, "Print our pgroup to stdout"},
+    {"print_fds", print_fds, "Print the list of active FDs to stdout"},
+    {"help", show_help, "Print list of fish_test_helper commands"},
+};
+
+static void show_help() {
+    printf("fish_test_helper: helper utility for fish\n\n");
+    printf("Commands\n");
+    printf("--------\n");
+    for (const auto &cmd : s_commands) {
+        printf("  %s:\n    %s\n\n", cmd.arg, cmd.desc);
+    }
+}
+
 int main(int argc, char *argv[]) {
+    std::sort(std::begin(s_commands), std::end(s_commands),
+              [](const fth_command_t &lhs, const fth_command_t &rhs) {
+                  return strcmp(lhs.arg, rhs.arg) < 0;
+              });
+
     if (argc <= 1) {
         fprintf(stderr, "No commands given.\n");
         return 0;
     }
     for (int i = 1; i < argc; i++) {
-        if (!strcmp(argv[i], "become_foreground_then_print_stderr")) {
-            become_foreground_then_print_stderr();
-        } else if (!strcmp(argv[i], "report_foreground")) {
-            report_foreground();
-        } else if (!strcmp(argv[i], "sigint_parent")) {
-            sigint_parent();
-        } else if (!strcmp(argv[i], "print_stdout_stderr")) {
-            print_stdout_stderr();
-        } else if (!strcmp(argv[i], "print_pid_then_sleep")) {
-            print_pid_then_sleep();
-        } else if (!strcmp(argv[i], "print_pgrp")) {
-            print_pgrp();
-        } else if (!strcmp(argv[i], "print_fds")) {
-            print_fds();
+        if (!strcmp(argv[i], "--help") || !strcmp(argv[i], "help") || !strcmp(argv[i], "-h")) {
+            show_help();
+            return 0;
+        }
+
+        const fth_command_t *found = nullptr;
+        for (const auto &cmd : s_commands) {
+            if (!strcmp(argv[i], cmd.arg)) {
+                found = &cmd;
+                break;
+            }
+        }
+        if (found) {
+            found->func();
         } else {
             fprintf(stderr, "%s: Unknown command: %s\n", argv[0], argv[i]);
             return EXIT_FAILURE;