Re: popen to a "pipe" utility ?

["Mark Edgar" <medgar123@...>]

On 2/17/07, gary ng <garyng2000@yahoo.com> wrote:
> Hi,
>
> I am wondering if there is a simple way to do this,
> that is popen("wc") then write things out to it and
> read back the result.

Not with popen.  However, with the "ex" API, you can implement this
easily enough:

require "ex"

function popen2(...)
 local in_rd, in_wr = io.pipe()
 local out_rd, out_wr = io.pipe()
 local proc, err = os.spawn{stdin = in_rd, stdout = out_wr, ...}
 in_rd:close(); out_wr:close()
 if not proc then
   in_wr:close(); out_rd:close()
   return proc, err
 end
 return proc, out_rd, in_wr
end

local p, i, o = assert(popen2("wc", "-w"))
o:write("Hello world"); o:close()
print(i:read"*l"); i:close()
p:wait()

See http://lua-users.org/wiki/ExtensionProposal

    -Mark