Perl : differences between double-quoted strings and single-quoted strings

#Perl : differences between double-quoted strings and single-quoted strings.

# Hello World Program in Perl

#

$string = "a string";

$text1 = "This is $string"; # becomes "This is a string"

$text2 = 'This is $string'; # remains 'This is $string'

$text3 = 'This string contains \', a quote character';

$text4 = 'This string ends with a backslash \\';

print "$text1 \n";

print "$text2 \n";

print "$text3 \n";

print "$text4 \n";


Result 
This is a string                                                                                                                                                                                    

This is $string                                                                                                                                                                                     

This string contains ', a quote character                                                                                                                                                           

This string ends with a backslash \