info command and man pages - linux

Question

Fedora 19 {though I doubt that's relevant]
If I invoke the info command for a topic that doesn't actually have an info node, but does have a man page, info will apparently create a node named (*manpages*)<topic> from the man page -- on the fly.
I can neither find this feature documented anywhere, nor (obviously) a description of how it's done.
Can anyone point me to some documentation about this?

Answer 1

I have checked the GNU standalone info manual and GNU Info manual and found nothing but a small sign that this feature exists. In the description of option --all we can read this:
--all
-a
Find all files matching the given menu-item (a file or node name).
Three usage patterns are supported, as follows.
First, if --all is used together with --where, info prints the names
of all matching files found on standard output (including *manpages*
if relevant) and exits.
So I'm afraid the only documentation is the source code. In info.c you can find the following function. Look for the "Fall back to loading man page." comment.
/* Get the initial Info file, either by following menus from "(dir)Top",
or what the user specifed with values in filename. */
static char *
get_initial_file (char *filename, int *argc, char ***argv, char **error)
{
char *initial_file = 0; /* First file loaded by Info. */
REFERENCE *entry;
/* If there are any more arguments, the initial file is the
dir entry given by the first one. */
if (!filename && (*argv)[0])
{
/* If they say info -O info, we want to show them the invocation node
for standalone info; there's nothing useful in info.texi. */
if (goto_invocation_p && (*argv)[0]
&& mbscasecmp ((*argv)[0], "info") == 0)
(*argv)[0] = "info-stnd";
entry = lookup_dir_entry ((*argv)[0], 0);
if (entry)
{
initial_file = info_find_fullpath (entry->filename, 0);
if (initial_file)
{
(*argv)++; /* Advance past first remaining argument. */
(*argc)--;
/* Store full path, so that we find the already loaded file in
info_find_file, and show the full path if --where is used. */
entry->filename = initial_file;
add_pointer_to_array (info_copy_reference (entry),
ref_index, ref_list, ref_slots, 2);
return initial_file;
}
}
}
/* User used "--file". */
if (filename)
{
initial_file = info_find_fullpath (filename, 0);
if (!initial_file)
{
if (filesys_error_number)
*error = filesys_error_string (filename, filesys_error_number);
}
else
return initial_file;
}
/* File name lookup. */
if (!filename && (*argv)[0])
{
/* Try finding a file with this name, in case
it exists, but wasn't listed in dir. */
initial_file = info_find_fullpath ((*argv)[0], 0);
if (initial_file)
{
(*argv)++; /* Advance past first remaining argument. */
(*argc)--;
return initial_file;
}
else
asprintf (error, _("No menu item `%s' in node `%s'."),
(*argv)[0], "(dir)Top");
}
/* Fall back to loading man page. */
if (filename || (*argv)[0])
{
NODE *man_node;
debug (3, ("falling back to manpage node"));
man_node = get_manpage_node (filename ? filename : (*argv)[0]);
if (man_node)
{
add_pointer_to_array
(info_new_reference (MANPAGE_FILE_BUFFER_NAME,
filename ? filename : (*argv)[0]),
ref_index, ref_list, ref_slots, 2);
initial_file = MANPAGE_FILE_BUFFER_NAME;
return initial_file;
}
}
/* Inexact dir lookup. */
if (!filename && (*argv)[0])
{
entry = lookup_dir_entry ((*argv)[0], 1);
if (entry)
{
(*argv)++; /* Advance past first remaining argument. */
(*argc)--;
/* Clear error message. */
free (*error);
*error = 0;
initial_file = info_find_fullpath (entry->filename, 0);
/* Store full path, so that we find the already loaded file in
info_find_file, and show the full path if --where is used. */
entry->filename = initial_file;
add_pointer_to_array (info_copy_reference (entry),
ref_index, ref_list, ref_slots, 2);
return initial_file;
}
}
/* Otherwise, we want the dir node. The only node to be displayed
or output will be "Top". */
return 0;
}
man.h contains the definition of MANPAGE_FILE_BUFFER_NAME:
#define MANPAGE_FILE_BUFFER_NAME "*manpages*"

Answer 2

info is a command like man, you can test the command : info make but info Read documentation in Info format.