[U-Boot] [PATCH] hush: when a variable expansion is empty, don't drop the parameter

[Russell King - ARM Linux]

On Thu, Feb 27, 2014 at 10:39:24AM +0000, Russell King - ARM Linux wrote:
> Standard shell will only drop an empty expansion if it's unquoted, so:
> 
> 	a="1 2 3"
> 	b=4
> 	c=
> 
> 	echo $a $b $c
> 
> ends up with arg1 = "1", arg2 = "2", arg3 = "3", arg4 = "4" and no arg5
> 
> 	echo "$a" "$b" "$c"
> 
> ends up with arg1 = "1 2 3", arg2 = "4", arg3 = "" and no arg4
> 
> 	echo "$a $b $c"
> 
> ends up with arg1 = "1 2 3 4 " and no arg2
> 
> If you'd like to check out this behaviour, this script will help you see
> each argument as it was passed by the shell.
> 
> #!/bin/sh
> n=1
> for a in "$@"; do
>   echo "arg$n: \"$a\""
>   n=$(($n + 1))
> done
> 
> Getting this right matters, because it affects stuff like the ability
> to make use of test -z / test -n, while preserving the ability to have
> unquoted empty variables disappear from argument lists.

There's another case where hush goes wrong:

echo "Longblah: $foo"
echo "Blah    : $foo"

should produce output where the :'s are aligned.  Does in standard shells,
but not in hush.  I suspect this is because the word splitting/expansion
isn't quite correct.  Words inside quotes should not be split even after
expansion - unless it's an expansion of "@".  Note that also fixes the
"$emptyvariable" problem at the root cause of the test -n/-z.

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