Re: MakeI(1): what means {} ?

["Christer Jansson" <christer%janssons.org@localhost>]

2008/2/16, James K. Lowden <jklowden%schemamania.org@localhost>:
> The make(1) man page explains (sort of) that "Targets and sources may
> contain the shell wildcard values.... The value `{}' need not necessarily
> be used to describe existing files."
>
> Eh?  Forgive me, but my sh(1) man page doesn't mention {} as a Shell
> Pattern, or as anything else for that matter.  (The term "wildcard" isn't
> used.  Nor is "glob", unfortunately.)
>

I didn't find anything about it in the NetBSD sh(1) man page, either.
I did however react on that it seems very brief  in comparison with
other sh(1) (or ksh(1) if you think it matters) man pages I've seen.

When I type "man sh" on my Mac OS X system, I get the bash(1) man page
(sh may actually start bash in posix-compliant mode which I guess
would be fair enough), and there, there is a heading "Brace expansion"
describing that feature. So *if* brace expansion is in the standard
(haven't read it that closely), *and* Mac OS X bash(1) gets it right,
*and* NetBSD also complies with the standard and gets it right, this
description will suffice:

   Brace Expansion
       Brace expansion is a mechanism by which arbitrary strings may be gener-
       ated.  This mechanism is similar to pathname expansion, but  the  file-
       names generated need not exist.  Patterns to be brace expanded take the
       form of an optional preamble, followed by a series  of  comma-separated
       strings  between  a pair of braces, followed by an optional postscript.
       The preamble is prefixed to each string contained  within  the  braces,
       and the postscript is then appended to each resulting string, expanding
       left to right.

       Brace expansions may be nested.  The results of  each  expanded  string
       are  not  sorted;  left  to  right  order  is  preserved.  For example,
       a{d,c,b}e expands into `ade ace abe'.

       Brace expansion is performed before any other expansions, and any char-
       acters  special to other expansions are preserved in the result.  It is
       strictly textual.  Bash does not apply any syntactic interpretation  to
       the context of the expansion or the text between the braces.

       A  correctly-formed  brace  expansion must contain unquoted opening and
       closing braces, and at  least  one  unquoted  comma.   Any  incorrectly
       formed  brace expansion is left unchanged.  A { or , may be quoted with
       a backslash to prevent its being considered part of a brace expression.
       To  avoid conflicts with parameter expansion, the string ${ is not con-
       sidered eligible for brace expansion.

       This construct is typically used as shorthand when the common prefix of
       the strings to be generated is longer than in the above example:

              mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace  expansion  introduces  a  slight incompatibility with historical
       versions of sh.  sh does not treat opening or closing braces  specially
       when  they  appear as part of a word, and preserves them in the output.
       Bash removes braces from words as a  consequence  of  brace  expansion.
       For  example,  a word entered to sh as file{1,2} appears identically in
       the output.  The same word is output as file1 file2 after expansion  by
       bash.   If strict compatibility with sh is desired, start bash with the
       +B option or disable brace expansion with the +B option to the set com-
       mand (see SHELL BUILTIN COMMANDS below).

This is obviously not present on the NetBSD sh(1) man page. Maybe the
guys maintaining it consider it an experimental feature and don't want
to doc it, maybe they just didn't find the time, or maybe they just
missed it.

> (btw, I was looking for a way to use make to say, "copy any files from
> dir1 to dir2 where the source file is more recent."  No luck so far.)

I don't remember make rules or syntax very well, not having had to
mess with it for a long time (closing in on a decade, actually!), but
if you specify each source file (in the target directory) as a make
target, and the files in the source directory as dependencies, and a
build command copying the source to the target, that should do the
trick. If you google for make tutorials you ought to find examples
doing just that. (Or even if you try other make(1) pages.)

Hope this helps.
-- 
Christer