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Syntax
Like any language, Perl has rules on how the code must be written for the interpreter to be able to read and execute the code. These rules are called syntax.

The basics of Perl syntax are demonstrated in the following short script. The script is simply various lines of code selected to demonstrate syntax concepts and are numbered solely for the purpose of reference in this tutorial. With Perl, lines are not normally numbered, although a line can be given a label.

     1   $a = "Hello";           # no type declaration, end with semicolon
     2   $a = 'Hello';           # same variable  assigned as a new data type
     3   $a =                    # 1st line of a 2-line code
     4        "Goodbye";         # 2nd line of a 2-line code
     5   $a = 5;                 # scalar given an integer value
     6   $a = 7.6;               # scalar given a floating point value
     7   @array = (1,"dog",4.2)  # array define by list of mixed types
     8   print (a$);             # parentheses around function arguments   
     9   print a$;               # parentheses optional  - "7.6" is printed
    10   print ("a$");           # interpolation - "7.6" is printed
    11   if ($a+1) {             # BLOCKS of code enclosed by { }
    12        print 'True';      # single quotes, no parenthesis
    13   }
    14   a$ = &Print_Hello       # calls subroutine Print_Hello
    15   sub Print_Hello {       # subroutine definition, no arguments
    16        print "Hello";
    17        return "done";     # a subroutine can return a value(s)
    18   }      
    19   if ($a) {print "true"}  # one line version of lines 14-16

     

Lines of Code
Perl scripts consist of lines of case-sensitive code which must end in a semicolon, as in Line 1. However because Perl ignores whitespace (spaces, tabs, line feeds), a line of code can be written to cover multiple lines of text, as shown in Lines 3 & 4. Line 19 shows how code can also be compacted onto a single line.

Comments
Any text to the right of a # character is treated as comments and is ignored during execution.

Variables
Perl variable names begin with $, @, or %. The basic variable type supported by Perl is the scalar variable, which starts with $, as in Line 1. A scalar may be a string, an integer, or a floating point number (Lines 1,5,6).

Arrays variable names begin with @. Hash variables names begin with %.

Perl builtin functions can recognize the type of data in a variable and will adjust their action accordingly.

Note that Perl is case-sensitive. The variables $dog and $DOG are two different variables.

Variable Definition
Unlike other languages, Perl does not require that you pre-define a variable or its type. To create a variable, simply use it in a line of code. The Perl interpreter can understand the type of data that is assigned to the variable and use it appropriately.

Strings & Quotes
String data may be enclosed in double or single quotes, as in Lines 1 & 2. However, double quotes offer the advantage of interpolating the content between the quotes, which means that variables will be replaced in the string with their value, as in Line 10.

Escape Characters
In addition to interpolation of variables inside a double quote, Perl also interpolates "escape characters", such as \n \' \" \\ \t. which correspond to a line feed, single quote, double quote, backslash, and tab.

Parentheses Parentheses ( ) are used in several ways by Perl. Parentheses may be used to enclose EXPRESSIONS, as shown in Line 14. An expression is code which resolves to a value. Parentheses are also use to enclose a list, as shown in Line 7. Finally, parentheses can be used to enclose arguments to a function but are optional as in Lines 8 & 9.

BLOCKS
Multiple lines of code may be enclosed by curly brackets { }. These are called BLOCKS of code, as shown in Lines 14-16. and Lines 15-19. Variables defined within a block do not exist outside that block (this is called scope). Code is arranged in blocks to identify code that must be executed in conjunction with functions such as "if" and "sub" statements (lines 11-13 and lines 15-18). A semicolon is not required after the last statement in a block (line 19), but it is considered good practice to use the semicolon anyway (line 17).

Blocks may also be given a label, which may be used in controlling the flow of program execution. See the flow control tutorial for more information.

Subroutines
A subroutine is defined using "sub" followed by the subroutine name, then the block of code to execute within the subroutine, as shown in Lines 15-18. Subroutine definitions do not include arguments because a program can pass any number of arguments to a subroutine. A subroutine is called by using & in front of the subroutine name, as in Line 14. Subroutines can be placed anywhere within the program. If the subroutine is placed before the line where it is called, the & is not required. A subroutine can return a value using a return statement (line 17).

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