difference?

Shell Programming and Scripting
1

Hi

what is the difference between following:

if [ condition ]
then
//some code
fi

AND

if test [ condition ]
then
//some code
fi

2

if ... requires a program to run, it then tests the exit code of the process to determine which branch to take.

test is a program which returns an exit code based of various expressions given as arguments.

[ actually a program look for /bin/[ or /usr/bin/[ in the file system, this is often a link to the program "test".

So "if test [" is actually like saying "if test test" or even "if /bin/test /bin/test".

The following is from Mac OSX 10.4.9...

$ ls -l /bin/test /bin/[
-r-xr-xr-x   2 root  wheel  18104 Mar 21  2005 /bin/[
-r-xr-xr-x   2 root  wheel  18104 Mar 21  2005 /bin/test
3

The second one is invalid.
Valid syntax :

if test condition
then
   //some code
fi
4

[ -z this ]

is just shorthand for

test -z this

they are exactly equivalent
man test