In bash, what is the difference between a null string and an empty string?

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In bash, what is the difference between a null string and an empty string?

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#1 by (1 votes)

1

I would like to know if there is a difference in how bash represents variables with null values

var=

and with empty strings

var=""

What precautions should I take when handling variables like these?

linux bash unix shell

asked by anonymous 24.12.2016 / 20:33

1 answer

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score 1 · Answer 1

Consider the following:

var1=

var2=""

The variable var1 has no value, has its value null ( null ). A null value is exactly a "NOTHING"! Different from the value of the var2 variable that has a blank string.

Imagine that we will be using some object language (just to stay more didactic). Using the example with Python:

$ python
Python 2.7.12 (default, Jun 29 2016, 14:05:02) 
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> var1 = None
>>> var2 = ""
>>> type(var1)
<type 'NoneType'>
>>> type(var2)
<type 'str'>

ps: None in python is the same as null in other languages.

The var1 situation demonstrates that there is no initialization of a value. So, a "nothing" can not receive a return, if you try ... you will get the famous error NullPointerException because nothingness can not receive attribute (s): it does not receive values and points to nothing.

>>> len(var1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'NoneType' has no len()

% w /% is a variable of type var2 empty. Something "empty" has its value of zero because this way the variable is initialized. That is, even being a "blank character" it has its place reserved in memory. Then, when using string (length) will be returned len() :

>>> len(var2)
0