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Scalars and Operators

In this second part of a five-part series on scalars in Perl, you'll learn about operators (both arithmetic and bitwise), among other things. This article is excerpted from chapter two of the book Beginning Perl, written by James Lee (Apress; ISBN: 159059391X).

TABLE OF CONTENTS:
  1. Scalars and Operators
  2. Converting Between Numbers and Strings
  3. Operators
  4. Bitwise Operators
By: Apress Publishing
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April 01, 2010

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Alternative Delimiters

That’s all very well, of course, until we want a / in the string. Suppose we want to replace “Slashdot” with “/.”—now we’re back where we started, having to escape things again. Thankfully, Perl allows us to choose our own delimiters so we don’t have to stick with//. Any nonalphanumeric (that is, nonalphabetic and nonnumeric) character can be used as a delimiter, provided it’s the same on both sides of the text. Furthermore, you can use{},[],(), and<>as left and right delimiters. Here’s a few ways of doing theprint qq/.../;, all of which have the same effect:

#!/usr/bin/perl -w
# quotes6.pl

print qq|'"Hi," said Jack. "Have you read /. today?"'\n|;
print qq#'"Hi," said Jack. "Have you read /. today?"'\n#;
print qq('"Hi," said Jack. "Have you read /. today?"'\n);
print qq<'"Hi," said Jack. "Have you read /. today?"'\n>;

We’ll see more of these alternative delimiters when we start working with regular expressions.

Here-Documents

There’s one final way of specifying a string—by means of a here-document. This idea was taken from the Unix shell, and works on any platform. Effectively, it means that you can write a large amount of text within your program, and it will be treated as a string provided it is identified correctly. Here’s an example:

#!/usr/bin/perl -w
# heredoc.pl

print <<EOF;

This is a here-document. It starts on the line after the two arrows,
and it ends when the text following the arrows is found at the beginning
of a line, like this:

EOF

A here-document must start with<<and then a label. The label can be anything, but is traditionallyEOF (end of file) orEOT(end of text). The label must immediately follow the arrows with no spaces between, unless the same number of spaces precedes the end marker. It ends when the label is found at the beginning of a line. In our case, the semicolon does not form part of the label, because it marks the end of theprint()function call.

By default, a here-document works like a double-quoted string. In order for it to work like a single-quoted string, surround the label in single quotes. This will become important when variable interpolation comes into play, as we’ll see later on.



 
 
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