[help] add an option to just display the internal help text

Fixes #67

lnav.1

@@ -46,6 +46,9 @@ Quit the program.
 \fB\-h\fR
 Print help and exit
 .TP
+\fB\-H\fR
+Display the internal help text.
+.TP
 \fB\-d\fR file
 Write debug messages to the given file.
 .TP

src/lnav.cc

@@ -2323,6 +2323,7 @@ static void usage(void)
         "\n"
         "Options:\n"
         "  -h         Print this message, then exit.\n"
+        "  -H         Display the internal help text.\n"
         "  -C         Check configuration and then exit.\n"
         "  -d file    Write debug messages to the given file.\n"
         "  -V         Print version information.\n"
@@ -3082,6 +3083,10 @@ static void looper(void)
                         HELP_MSG_2(f, F,
                                    "to switch to the next/previous file"));
                 }
+                if (!initial_build && lnav_data.ld_flags & LNF_HELP) {
+                    toggle_view(&lnav_data.ld_views[LNV_HELP]);
+                    initial_build = true;
+                }
                 if (lnav_data.ld_log_source.text_line_count() > 0 ||
                     lnav_data.ld_text_source.text_line_count() > 0) {
                     initial_build = true;
@@ -3655,13 +3660,17 @@ int main(int argc, char *argv[])
     lnav_data.ld_looping        = true;
     lnav_data.ld_mode           = LNM_PAGING;
     lnav_data.ld_debug_log_name = "/dev/null";
-    while ((c = getopt(argc, argv, "harsCd:tw:V")) != -1) {
+    while ((c = getopt(argc, argv, "hHarsCd:tw:V")) != -1) {
         switch (c) {
         case 'h':
             usage();
             exit(retval);
             break;
 
+        case 'H':
+            lnav_data.ld_flags |= LNF_HELP;
+            break;
+
         case 'C':
             exit(0);
             break;
@@ -3779,7 +3788,7 @@ int main(int argc, char *argv[])
         }
     }
 
-    if (lnav_data.ld_file_names.empty()) {
+    if (lnav_data.ld_file_names.empty() && !lnav_data.ld_flags & LNF_HELP) {
         fprintf(stderr, "error: no log files given/found.\n");
         retval = EXIT_FAILURE;
     }

src/lnav.hh

@@ -70,11 +70,11 @@ typedef enum {
 
 enum {
     LNB_SYSLOG,
-    LNB_TIMESTAMP,
-
     LNB__MAX,
 
-    LNB_ROTATED
+    LNB_TIMESTAMP,
+    LNB_HELP,
+    LNB_ROTATED,
 };
 
 /** Flags set on the lnav command-line. */
@@ -84,8 +84,9 @@ typedef enum {
     LNF_ROTATED   = (1L << LNB_ROTATED),
 
     LNF_TIMESTAMP = (1L << LNB_TIMESTAMP),
+    LNF_HELP      = (1L << LNB_HELP),
 
-    LNF__ALL      = (LNF_SYSLOG)
+    LNF__ALL      = (LNF_SYSLOG|LNF_HELP)
 } lnav_flags_t;
 
 /** The different views available. */