| 1 | =head1 NAME
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| 2 | X<syntax>
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| 3 |
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| 4 | perlsyn - Perl syntax
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| 5 |
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| 6 | =head1 DESCRIPTION
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| 7 |
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| 8 | A Perl program consists of a sequence of declarations and statements
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| 9 | which run from the top to the bottom. Loops, subroutines and other
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| 10 | control structures allow you to jump around within the code.
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| 11 |
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| 12 | Perl is a B<free-form> language, you can format and indent it however
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| 13 | you like. Whitespace mostly serves to separate tokens, unlike
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| 14 | languages like Python where it is an important part of the syntax.
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| 15 |
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| 16 | Many of Perl's syntactic elements are B<optional>. Rather than
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| 17 | requiring you to put parentheses around every function call and
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| 18 | declare every variable, you can often leave such explicit elements off
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| 19 | and Perl will figure out what you meant. This is known as B<Do What I
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| 20 | Mean>, abbreviated B<DWIM>. It allows programmers to be B<lazy> and to
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| 21 | code in a style with which they are comfortable.
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| 22 |
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| 23 | Perl B<borrows syntax> and concepts from many languages: awk, sed, C,
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| 24 | Bourne Shell, Smalltalk, Lisp and even English. Other
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| 25 | languages have borrowed syntax from Perl, particularly its regular
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| 26 | expression extensions. So if you have programmed in another language
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| 27 | you will see familiar pieces in Perl. They often work the same, but
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| 28 | see L<perltrap> for information about how they differ.
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| 29 |
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| 30 | =head2 Declarations
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| 31 | X<declaration> X<undef> X<undefined> X<uninitialized>
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| 32 |
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| 33 | The only things you need to declare in Perl are report formats and
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| 34 | subroutines (and sometimes not even subroutines). A variable holds
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| 35 | the undefined value (C<undef>) until it has been assigned a defined
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| 36 | value, which is anything other than C<undef>. When used as a number,
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| 37 | C<undef> is treated as C<0>; when used as a string, it is treated as
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| 38 | the empty string, C<"">; and when used as a reference that isn't being
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| 39 | assigned to, it is treated as an error. If you enable warnings,
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| 40 | you'll be notified of an uninitialized value whenever you treat
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| 41 | C<undef> as a string or a number. Well, usually. Boolean contexts,
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| 42 | such as:
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