Re: Bug in [ -d ... ] ?

[Greg Wooledge]

On Thu, Nov 02, 2017 at 11:03:27AM +0000, Michael F Gordon wrote:
> Can anyone explain the following?
> 
> tla19> set|grep FOOFOOFOO
> tla19> if [ -d ${FOOFOOFOO:=""} ]; then echo YES;fi
> YES

Quoting failure.

wooledg:~$ unset FOO
wooledg:~$ if [ -d "${FOO:=""}" ]; then echo yes; else echo no; fi
no

With quotes the command is transformed to

[ -d "" ]

Without quotes it becomes

[ -d ]

A single-argument test command simply checks whether the string (-d in
this case) is nonzero length.  It is equivalent to

[ -n -d ]