Bourne shell "if" syntax

[lconrad at go2france.com]

script fragment:

PTR=`dig @some.dns +short +norec -x a.b.c.d`

echo "$PTR"

if  [  "$PTR"  ==  ""  ]  ;  then

echo "$PTR" >> /path/to/PTR_absent.txt

fi

===========

output for an IP:


a-b-c-d.domain.net.
[: a-b-c-d.domain.net.: unexpected operator

thanks
Len