Word separation occurs even with double quotes

Question

According to http://tldp.org/LDP/abs/html/quotingvar.html

Use double quotation marks to prevent word breaks. The argument enclosed in double quotation marks is a single word, even if it contains space delimiters.

However i have

0> /bin/bash --version
GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu)
[...]

1> cat inspect.sh 
#!/bin/bash
echo "first argument is $1"
echo "second argument is $2"

2> cat test.sh 
#!/bin/bash
set -x
./inspect.sh "hello $@"

3> ./test.sh alice bob
+ ./inspect.sh 'hello alice' bob
first argument is hello alice
second argument is bob

4> ./test.sh "alice bob"
+ ./inspect.sh 'hello alice bob'
first argument is hello alice bob
second argument is 

I am wondering why 3> and 4> have different results? How to change test.sh so that 3> have the same result as 4>?

Answer 1

Answer: $@is special.

In the Bash Reference Guide 3.4.2 Special Parameters:

@

, . , . , "$ @" "$ 1" "$ 2".... , , . , "$ @" $@ (.. ).

:

• , .

• , , .

"hello ", , "" , .

, $*.

*

, . , , IFS. "$ *" "$ 1c $2c...", c - IFS. IFS , . IFS NULL, .