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Subject: Re: Programatically finding value of "cygdrive" prefix
From: Hannu E K Nevalainen <_garbage_collector_ AT telia DOT com>
To: cygwin AT cygwin DOT com
In-Reply-To: <Pine.GSO.4.61.0508152130380.9560@slinky.cs.nyu.edu>
References: <42FA4604 DOT 8000507 AT tlinx DOT org> 	 <20050810183616 DOT GA5892 AT trixie DOT casa DOT cgf DOT cx> 	 <Pine DOT GSO DOT 4 DOT 61 DOT 0508152130380 DOT 9560 AT slinky DOT cs DOT nyu DOT edu>
Content-Type: text/plain
Date: Tue, 16 Aug 2005 22:04:40 +0200
Message-Id: <1124222681.29974.37.camel@p450>
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On Mon, 2005-08-15 at 21:43 -0400, Igor Pechtchanski wrote:
> On Wed, 10 Aug 2005, Christopher Faylor wrote:
> 
> > On Wed, Aug 10, 2005 at 11:23:00AM -0700, Linda W wrote:
> > >Is there a way to find out in a bash script the cygdrive prefix?
> > >I thought something simple like
> > >   mount -p|tail -1|cut -f1
> > >but that incorrectly assumed the fields were tab delimited.
> > >Since there can be spaces in the cygdrive prefix, I can't
> > >use space a delimiter, example:
> > ># mount -p
> > >Prefix              Type         Flags
> > >/cyg drive posix path  system       binmode
> > >----
> >
> > There may be a simpler way to do it, but this seems to work:
> >
> > mount -p | sed -n '2s/\([^ ]\)  *[^ ][^ ]*  *[^ ][^ ]*$/\1/p'
> 
> The main question is: *why* would one want to programmatically find out
> the cygdrive prefix?

You're making assumptions without insight, Igor. Please, don't assume!
Be open minded and allow to extract the information in an easily
accessible manner - PLEASE.

In general, having a setting be "hidden" in the manner that the cygdrive
prefix is - is a bad idea. Simply because you never know what other ppl
might come up with, if it IS accessible.

Allowing RE-Reading the value of a parameter, that can be set, should
IMO never be restricted, unless maybe the restricting is based on
security... (passwords comes to mind)

Check my local example "cygdrive" use below. Not perfect, but works - as
it is - in my very static cygwin setup (e.g. has problems w spaces under
certain conditions, a condition NOT present on my computers; I'm rabid
on this)

NOTE: A digital camera shows up as an USB drive, i.e. a DOS drive ->
e.g. /cygdrive/<next free letter> - and is available so long as the
camera stays ON (it eventually WILL go OFF after last use, just as your
screen blanker! Depending on how you've set it or use it.)


> If all you want is access '/cygdrive/c' via a POSIX path, wouldn't
> "cygpath -u c:" do the right thing?  In fact, barring special mounts,
> "cygpath -u c:|sed 's#/c$##'" should do what the OP asked.

Are you sure there is a C: drive on every Windows computer, I wouldn't
wager on that.

> Alternatively, one could actually use the quotes that "mount -m" produces,
> via something like
> 
> mount -m | grep -- --change-cygdrive-prefix | \
>   xargs bash -c 'while [ $# != 1 ]; do shift; done; echo "$@"' --
> 

IMO, something like
$ mount -m | grep 'cygdrive-prefix' | sed -rne 's/.*"(.*)".*/\1/p'

should work ; UNTESTED (I'm on Linux right now)


---8<--- example use ---

[henk AT p450 scripts]$ cat digicam
#!/bin/bash

# (C) Copyright 2003-10-29 by Hannu E K Nevalainen, Mariefred, Sweden
# With the exception of the copyright, this script is
# free with the restrictions set by the fsf.org GPL.

# Prerequisites:
# MANY digital still image cameras connect to a host computer
# via e.g. USB, and thus show up as one extra mass storage device.
# This device contains a _standardized_ directory tree. One of the
# facts is that there is a DCIM folder in the root.
# The DCIM folder contains at least yet one level of folders
# which in turn will contain the images. These can be either
# *.JPG *.MOV and presumably *.TIF (I'm not aware of others)
#
# The script first finds out currently mounted DOS/WINDOWS devices.
# Then loops through these looking for the root DCIM-folder...
# those that contain the folder will have their cygwin path printed.

for i in $(cygdrives) ;do
  if [ -d $i/DCIM ] ;then
    echo $i;
  fi;
done

[henk AT p450 scripts]$ cat cygdrives
#!/bin/bash

# (C) 2003-10-29 by Hannu E K Nevalainen, Mariefred, Sweden
#
# show paths to all mounted DOS/WINDOWS devices.

mount | grep -E "$(cygprefix)[a-z] " | cut -d" " -f3

[henk AT p450 scripts]$ cat cygprefix
#!/bin/bash

# (C) 2003-10-29 by Hannu E K Nevalainen, Mariefred, Sweden
#
# grep out the cygwin prefix for DOS/WINDOWS devices

mount -p |
tail -1 |
(
  read p z;
  if [ ! "${p: -1}" == "/" ] ;then
    p="$p/";
  fi;
  echo "$p"
)

[henk AT p450 scripts]$

/Hannu E K Nevalainen


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