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Subject: RE: dumb escaping question when using Cygwin +  NT commands
Date: Thu, 19 Sep 2002 12:23:33 -0400
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From: "Scott Prive" <Scott DOT Prive AT storigen DOT com>
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Yes that helped; thanks.

> -----Original Message-----
> From: Igor Pechtchanski [mailto:pechtcha AT cs DOT nyu DOT edu]
> Sent: Thursday, September 19, 2002 12:00 PM
> To: Scott Prive
> Cc: cygwin AT cygwin DOT com
> Subject: RE: dumb escaping question when using Cygwin + NT commands
> 
> 
> On Thu, 19 Sep 2002, Scott Prive wrote:
> 
> > I assumed quotes controlled how data gets sent to commands, but
> > apparently that's an oversimplification: quotes protect 
> data being sent
> > to a NEW PROCESS.. and builtins like "echo" are NOT a new 
> process (`type
> > echo). This explains why the echo command understood what 
> the heck was
> > inside '$2', but the echo command did not.
> 
> Not quite.  In most shells, the builtin commands are 
> subjected to the same
> quoting rules as the external commands (there are some 
> exceptions, but I
> believe echo isn't one of them).  What was happening in your 
> case was that
> on the echo command line, the shell was getting single quotes inside
> double quotes, and thus treated them as regular characters 
> (expanding the
> vars within the DOUBLE quotes).  When you called your program, on the
> other hand, the shell was getting the variables in SINGLE quotes only,
> thus avoiding the expansion.
> 
> You should have called both echo and net in the same way:
> 
>    net "$1" "$2" "$3" "$4" "$5"
>    echo "we saw in mount_drive2:" "$1" "$2" "$3" "$4" "$5"
> 
> or, better yet,
> 
>    [ $# -eq 5 ] || (echo "Invalid number of arguments" >&2 && exit 2)
>    net "$@"
>    echo "we saw in mount_drive2: $@"
> 
> Hope this helps.
> 	Igor
> 
> On Thu, 19 Sep 2002, Scott Prive wrote:
> 
> > > -----Original Message-----
> > > From: Randall R Schulz [mailto:rrschulz AT cris DOT com]
> > > Sent: Wednesday, September 18, 2002 6:30 PM
> > > To: cygwin AT cygwin DOT com
> > > Subject: Re: dumb escaping question when using Cygwin + 
> NT commands
> > >
> > >
> > > Scott,
> > >
> > > At 15:15 2002-09-18, Scott Prive wrote:
> > >
> > > >Hello,
> > > >
> > > >I get this odd problem when calling NT commands from Cygwin. I am
> > > >single-quoting the data, but the way I'm doing things
> > > (probably wrong...)
> > > >does not like passing $1 function arguments to NT commands.
> > > If I hardcode
> > > >the arguments internally, everything works.
> > > >
> > > >The two example functions below are intended to behave identical.
> > > >
> > > >#!/bin sh
> > > >
> > > >mount_drive () {
> > > >    # Syntax: net 'use' '*' '\\redhat\foo' 'foo' '/user:foo'
> > > >    net 'use' 'F:' '\\redhat\foo' 'foo' '/user:foo'
> > > >
> > > >    echo "The command returned $?"
> > > >    return $?;
> > > >}
> > >
> > > Note that the status ($?) you're returning from the
> > > "mount_drive" shell
> > > procedure is that of the "echo" command, not that printed
> > > _by_ the echo
> > > command.
> > >
> > > The only arguments in this example for which quoting 
> changes the net
> > > argument passed to the underlying command is the one that
> > > includes "redhat"
> > > and the asterisk. The others contain no special 
> characters requiring
> > > quoting or escaping to inhibit special interpretation.
> > >
> > >
> > > >mount_drive2 () {
> > > >    net '$1' '$2' '$3' '$4' '$5'
> > > >    echo "we saw in mount_drive2: '$1' '$2' '$3' '$4' '$5' "
> > > >
> > > >    echo "The command returned $?"
> > > >    return $?;
> > > >}
> > >
> > > The same "$?" issue exists here, of course.
> > >
> > > You need to be aware of the difference between 'single
> > > quotes' and "double
> > > quotes." Variable expansion is inhibited in single-quoted
> > > arguments, but
> > > not in double-quoted ones. Furthermore, double quoted
> > > arguments protect
> > > single quotes, making the non-special. So you've probably
> > > confused yourself
> > > into thinking that in this example the "net" command saw the
> > > arguments you
> > > passed to the "mount_drive2" procedure. It did not. It saw
> > > arguments each
> > > consisting of a dollar sign followed by a digit. Then you
> > > echoed a single
> > > argument composed of some fixed text, some single quote marks
> > > and some
> > > expanded positional parameters.
> >
> > Doh!
> >
> > Thanks. A good nights sleep and coffee got me thinking 
> about this on the
> > way to work, and then I read your post.
> >
> > I misled myself because the ECHO command "worked". A debugging habit
> > from Perl is I would print out my variables. Since the echo 
> worked, I
> > never questioned what I was doing with quotes.
> >
> > I assumed quotes controlled how data gets sent to commands, but
> > apparently that's an oversimplification: quotes protect 
> data being sent
> > to a NEW PROCESS.. and builtins like "echo" are NOT a new 
> process (`type
> > echo). This explains why the echo command understood what 
> the heck was
> > inside '$2', but the echo command did not.
> >
> > Of course you know this; I'm just filling in the blanks for 
> the benefit
> > of mailing list and Google searches. For all of last night, 
> I actually
> > believed the problem was due to mixing NT commands and Cygwin.
> >
> > Thanks again.
> >
> > >
> > >
> > > >#
> > > >mount_drive
> > > >mount_drive2 'use' 'G:' '\\redhat\foo' 'foo' '/user:foo'
> > > >############# END SCRIPT
> > > >
> > > >
> > > >the output I get from mount_drive2 is standard "usage info",
> > > indicating I
> > > >passed arguments incorrectly. However the debug echo 
> *looks* correct.
> > > >
> > > >Someone please point out my mistake, else I'm doomed to some
> > > ugly hackish
> > > >workarounds ;-)
> > > >
> > > >Thanks,
> > > >
> > > >Scott
> > >
> > >
> > > Randall Schulz
> > > Mountain View, CA USA
> > >
> > >
> > > --
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> > >
> >
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> >
> 
> -- 
> 				http://cs.nyu.edu/~pechtcha/
>       |\      _,,,---,,_		pechtcha AT cs DOT nyu DOT edu
> ZZZzz /,`.-'`'    -.  ;-;;,_		igor AT watson DOT ibm DOT com
>      |,4-  ) )-,_. ,\ (  `'-'		Igor Pechtchanski
>     '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!
> 
> "Water molecules expand as they grow warmer" (C) Popular 
> Science, Oct'02, p.51
> 
> 

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