perf list: Remove blank lines, headers when piping output

So that one can, for instance, use it with wc -l:

  # perf list *:*write* | wc -l
  60

Or to look for the "bio" tracepoints, without 'perf list' headers:

  # perf list *:*bio* | head
    block:block_bio_backmerge                          [Tracepoint event]
    block:block_bio_bounce                             [Tracepoint event]
    block:block_bio_complete                           [Tracepoint event]
    block:block_bio_frontmerge                         [Tracepoint event]
    block:block_bio_queue                              [Tracepoint event]
    block:block_bio_remap                              [Tracepoint event]
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ts7sc0x8u4io4cifzkup4j44@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-list.c

@@ -36,7 +36,7 @@ int cmd_list(int argc, const char **argv, const char *prefix __maybe_unused)
 
 	setup_pager();
 
-	if (!raw_dump)
+	if (!raw_dump && pager_in_use())
 		printf("\nList of pre-defined events (to be used in -e):\n\n");
 
 	if (argc == 0) {

tools/perf/util/parse-events.c

@@ -1534,7 +1534,7 @@ restart:
 		printf("  %-50s [%s]\n", evt_list[evt_i++],
 				event_type_descriptors[PERF_TYPE_TRACEPOINT]);
 	}
-	if (evt_num)
+	if (evt_num && pager_in_use())
 		printf("\n");
 
 out_free:
@@ -1690,7 +1690,7 @@ restart:
 		printf("  %-50s [%s]\n", evt_list[evt_i++],
 				event_type_descriptors[PERF_TYPE_HW_CACHE]);
 	}
-	if (evt_num)
+	if (evt_num && pager_in_use())
 		printf("\n");
 
 out_free:
@@ -1763,7 +1763,7 @@ restart:
 		}
 		printf("  %-50s [%s]\n", evt_list[evt_i++], event_type_descriptors[type]);
 	}
-	if (evt_num)
+	if (evt_num && pager_in_use())
 		printf("\n");
 
 out_free:
@@ -1804,13 +1804,14 @@ void print_events(const char *event_glob, bool name_only)
 		printf("  %-50s [%s]\n",
 		       "cpu/t1=v1[,t2=v2,t3 ...]/modifier",
 		       event_type_descriptors[PERF_TYPE_RAW]);
-		printf("   (see 'man perf-list' on how to encode it)\n");
-		printf("\n");
+		if (pager_in_use())
+			printf("   (see 'man perf-list' on how to encode it)\n\n");
 
 		printf("  %-50s [%s]\n",
 		       "mem:<addr>[/len][:access]",
 			event_type_descriptors[PERF_TYPE_BREAKPOINT]);
-		printf("\n");
+		if (pager_in_use())
+			printf("\n");
 	}
 
 	print_tracepoint_events(NULL, NULL, name_only);

tools/perf/util/pmu.c

@@ -1026,7 +1026,7 @@ void print_pmu_events(const char *event_glob, bool name_only)
 		printf("  %-50s [Kernel PMU event]\n", aliases[j]);
 		printed++;
 	}
-	if (printed)
+	if (printed && pager_in_use())
 		printf("\n");
 out_free:
 	for (j = 0; j < len; j++)