scripts

[Uwe Kleine-König]

On Tue, Mar 01, 2011 at 04:20:25PM +0200, Baruch Siach wrote:
> Hi Marc,
> 
> On Tue, Mar 01, 2011 at 03:11:31PM +0100, Marc Kleine-Budde wrote:
> > On 03/01/2011 03:06 PM, Vanalme Filip wrote:
> > [...]
> > 
> > > One more question about barebox scripts (I guess even scripts in
> > > general...). This is part of a script from another board (that I took
> > > over for my own board):
> > 
> > > #!/bin/sh
> > > 
> > > . /env/config
> > > 
> > > If [ x$1 = xflash ]; then
> > > 	root=flash
> > > 	kernel=flash
> > > fi
> > > 
> > > if [ x$1 = xnet ]; then
> > > 	root=net
> > > 	kernel=net
> > > fi
> > > 
> > > why the scripts are using i.e. [ x$1 = xflash ] instead of just simply [ $1 = flash ] ? Both are doing the same, no ?
> > 
> > The shell is quite old and doesn't support that. But you're right for
> > modern shells like bash or dash.
> 
> I get this under bash:
> 
> $ [ $UNDEF = test ]
> bash: [: =: unary operator expected
> 
> However '[ "$UNDEF" = test ]' behaves as expected under bash (but not under 
> hush, which is the shell of Barebox).
I didn't test it, but even if a variable is defined, I guess this might
result in trouble:

	arg=-n
	[ $arg = flash ]

(At least I remember this being the reason for using "x$arg" back when I
worked on Solaris.)

And note without quoting quite interesting things can happen, e.g.:

	test -n $arg

returns false if arg="= 42".

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |