{"id":77772,"date":"2020-01-22T16:43:12","date_gmt":"2020-01-22T11:13:12","guid":{"rendered":"https:\/\/www.vskills.in\/certification\/tutorial\/?p=77772"},"modified":"2024-04-12T14:29:55","modified_gmt":"2024-04-12T08:59:55","slug":"datatypes-and-variables","status":"publish","type":"page","link":"https:\/\/www.vskills.in\/certification\/tutorial\/datatypes-and-variables\/","title":{"rendered":"Datatypes and Variables"},"content":{"rendered":"

Datatypes and Variables<\/strong><\/h4>\n

NASL allows for the assignment of values to variables that can be manipulated by a NASL script. Unlike a strongly typed language such as C, NASL does not require you to predefine a variable’s type. In NASL, the variable type is determined automatically when a variable is assigned a specific value. NASL recognizes two valid datatypes: scalars and arrays. A scalar can be a number or a string, while an array is a collection of scalars.<\/p>\n

Numbers: <\/strong>NASL allows variables to hold integer values\u2014for example, the number 11. It is also possible to assign numeric values to variables using a hexadecimal representation. You write hexadecimal numbers in NASL using a leading “0x” prefix. For example, the hexadecimal number 0x1b holds the value 27 when represented as an integer in base-10 notation. Type the following script into a file:<\/p>\n

\u00a0<\/strong><\/p>\n

h=0x1b;<\/p>\n

display (“The value of h is “,h,”\\n”);<\/p>\n

Now run it using the NASL interpreter to see the output:<\/p>\n[notroot]$ nasl hex.nasl<\/p>\n

The value of h is 27<\/p>\n

It is also possible to input numerical values in octal notation form, which uses base- 8 notation by placing a leading “0” prefix. For example, the x and y are equivalent in the following example:<\/p>\n

x=014; #octal<\/p>\n

y=12; #decimal<\/p>\n

Strings: <\/strong>A string is a collection of characters. abcdefg, Hello World, and Boeing 747 are all examples of strings. Consider the following NASL script:<\/p>\n

mystring=”Hello. I am a string!\\n”;<\/p>\n

display(mystring);<\/p>\n

The \\n at the end of mystring is an escape character and is equivalent to a newline character. Table 1-1 lists common escape characters applicable to NASL.<\/p>\n

Table 1-1. Escape characters<\/strong><\/p>\n

\"image013\"<\/p>\n

Note that a string inside double quotes (“) is left as is. Therefore, if you define a string using double quotes, escape sequences will not be translated. Also note that the display( ) function calls the string( ) function before displaying data on the console, and it is the string( ) function that converts the escape sequences. That is why our escape sequences are translated in the preceding examples even though we define them using double quotes.<\/p>\n

Arrays and Hashes: <\/strong>An array is a collection of numbers or strings that can be indexed using a numeric subscript. Consider the following NASL script:<\/p>\n

myarray=make_list(1,”two”);<\/p>\n

display(“The value of the first item is “,myarray[0],” \\n”);<\/p>\n

display(“The value of the second item is “,myarray[1],” \\n”);<\/p>\n

The script displays the following when executed:<\/p>\n

The value of the first item is 1<\/p>\n

The value of the second item is two<\/p>\n

Notice that the array subscripts begin at 0, and that is why the first element is obtained using the [0] subscript.<\/p>\n

Like arrays, hashes are also collections of numbers or strings. However, elements in hashes have a key value associated with them that can be used to obtain the element. You can use the make_array( ) function call to define a hash. Because every element must have an associated key value, the function call requires an even number of arguments. The following is a definition of a hash that contains port numbers for the Telnet protocol (port 23) and HTTP (port 80):<\/p>\n

myports=make_array(‘telnet’,23,’http’,80);<\/p>\n

Now, myports[‘telnet’] gives you the value of 23, while myports[‘http’] evaluates to 80.<\/p>\n

Local and Global Variables<\/strong><\/p>\n

Variables exist only within the blocks in which they are defined. A block is a collection of statements enclosed by special statements such as loops and function calls. For example, if you define a variable within a particular function call, it will not exist when the function call returns. At times, it is necessary to define variables that should exist globally; in such cases you should use global_var to define them:<\/p>\n

global_var myglobalvariable;<\/p>\n

Variables are local by default. You can also use local_var to state this explicitly.<\/p>\n

Apply for Network Security Open Source Software Developer Certification Now!!<\/h3>\n

https:\/\/www.vskills.in\/certification\/network-security-open-source-software-developer-certification<\/a><\/p>\n

Back to Tutorial<\/a><\/strong><\/h4>\n","protected":false},"excerpt":{"rendered":"

Datatypes and Variables NASL allows for the assignment of values to variables that can be manipulated by a NASL script. Unlike a strongly typed language such as C, NASL does not require you to predefine a variable’s type. In NASL, the variable type is determined automatically when a variable is assigned a specific value. NASL…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"categories":[9066],"tags":[9072],"class_list":["post-77772","page","type-page","status-publish","hentry","category-network-security-open-source","tag-datatypes-and-variables"],"acf":[],"yoast_head":"\nDatatypes and Variables - Tutorial<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.vskills.in\/certification\/tutorial\/datatypes-and-variables\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Datatypes and Variables - Tutorial\" \/>\n<meta property=\"og:description\" content=\"Datatypes and Variables NASL allows for the assignment of values to variables that can be manipulated by a NASL script. Unlike a strongly typed language such as C, NASL does not require you to predefine a variable’s type. In NASL, the variable type is determined automatically when a variable is assigned a specific value. 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