If you come across this question trying to install Ruby using Ruby Version Manager (RVM) on Ubuntu 10.04 then there are instructions on installing zlib on the rvm web site http://rvm.beginrescueend.com/packages/zlib/
The steps are:
rvm pkg install zlib
(or
rvm package install zlib if you get "ERROR: Unrecognized command line argument: 'pkg'" - older versions of rvm used the verb 'package' instead)
then
rvm remove 1.9.1
rvm install 1.9.1
.nil? can be used on any object and is true if the object is nil.
.empty? can be used on strings, arrays and hashes and returns true if:
- String length == 0
- Array length == 0
- Hash length == 0
Running .empty? on something that is nil will throw a NoMethodError.
That is where .blank? comes in. It is implemented by Rails and will operate on any object as well as work like .empty? on strings, arrays and hashes.
nil.blank? == true
false.blank? == true
[].blank? == true
{}.blank? == true
"".blank? == true
5.blank? == false
0.blank? == false
.blank? also evaluates true on strings which are non-empty but contain only whitespace:
" ".blank? == true
" ".empty? == false
Rails also provides .present?, which returns the negation of .blank?.
Array gotcha: blank? will return false even if all elements of an array are blank. To determine blankness in this case, use all? with blank?, for example:
[ nil, '' ].blank? == false
[ nil, '' ].all? &:blank? == true
Best Answer
There is now a linux equivalent: prax