Expanding @-pathnames from Cygwin bash

[Christopher Faylor]

On Wed, Feb 13, 2013 at 05:47:19PM +0000, Adam Dinwoodie wrote:
>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.

Right.  That web page says:

"To circumvent the limitations on shell line length in the native
Windows command shells..."

'@' parsing only happens when the Cygwin program is started from a non-Cygwin
program, e.g., CMD.EXE.  I've changed the docs to make it a little clearer.
This will show up on the web site eventually.

cgf

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