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From:	Adam Dinwoodie <Adam DOT Dinwoodie AT metaswitch DOT com>
To:	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject:	Expanding @-pathnames from Cygwin bash
Date:	Wed, 13 Feb 2013 17:47:19 +0000
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The UG states

> Cygwin programs expand their arguments starting with "@" in a special way. If
> a file pathname exists, the argument @pathname expands recursively to the
> content of pathname.
-- http://cygwin.com/cygwin-ug-net/using-specialnames.html#pathnames-at

It then contrasts "the behaviors of the bash built-in echo and of the program
/bin/echo."  The implication I read is that the bash built-in echo doesn't
expand @-arguments because it's a built-in, not a fully-fledged program.

However, this doesn't seem to be what's happening.  Running on my Cygwin system:

    $ echo 'Hi' >testfile
    $ echo 'Hi testfile' >args
    $ type grep
    grep is hashed (/usr/bin/grep)
    $ grep @args    #This hangs until I hit ^C, waiting for input
    
    $ echo '@args' | grep @args    #This shows grep looks for the literal string "@args"
    @args
    $ cmd
    Microsoft Windows [Version 6.1.7601]
    Copyright (c) 2009 Microsoft Corporation.  All rights reserved.
    
    C:\>c:\cygwin\bin\grep @args
    c:\cygwin\bin\grep @args
    Hi

By my reading of the UG, since grep is a Cygwin program, it should always
expand "@args" to the contents of the "args" file.  However this doesn't seem
to happen when grep is run from within bash, only within the Windows shell.

I think this is an error in the UG: my first guess is this behaviour is only
invoked when the parent process isn't a Cygwin process.  If so, the UG
shouldn't explain the behaviour in the example as being due to echo being a
bash built-in; that behaviour also occurs if you invoke echo.exe.

-- 
Adam Dinwoodie

Messages posted to this list are made in a personal capacity.



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