Single & Double Quotes and Here documents

Single & Double Quotes in Perl

You can use double quotes or single quotes around literal strings as follows:

#! /usr/bin/perl

print "Hello, world\n";

print 'Hello, world\n';

This will produce following result:

Hello, world

Hello, world\n$

There is important different in single and double quotes. Only double quotes interpolate variables and special characters such as new lines \n where as single quote does not interpolate any variable or special character. Check below example where we are using $a as a variable to store a value and later printing that value:

#!/usr/bin/perl

$a = 10;

print "Value of a = $a\n";

print 'Value of a = $a\n';

This will produce following result:

Value of a = 10

Value of a = $a\n$

"Here" Documents

You can store or print multi line text with a great comfort. Even you can make use of variables inside "here" document. Below is a simple syntax, check carefully there must be no space between the << and the identifier.
An identifier may be either a bare word or some quoted text like we used EOF below. If identifier is quoted, the type of quote you use determines the treatment of the text inside the here document, just as in regular quoting. An unquoted identifier works like double quotes.

#! /usr/bin/perl

$a = 10;

$var = <<"EOF";

This is the syntax for here document and it will continue

Until it encounters an EOF in the first line.

This is case of double quote so variable value will be 

Interpolated. For example value of a = $a

EOF

print "$var\n";

$var = <<'EOF';

This is case of single quote so variable value will not be 

Interpolated. For example value of a = $a

EOF

print "$var\n";

This will produce following result:

This is the syntax for here document and it will continue

until it encounters a EOF in the first line.

This is case of double quote so variable value will be

Interpolated. For example value of a = 10

This is case of single quote so variable value will not be

Interpolated. For example value of a = $a