string - What's the difference between single and double quotes in Perl?

Question

In Perl, what is the difference between ' and " ?

For example, I have 2 variables like below:

$var1 = '(';
$var2 = "(";

$res1 = ($matchStr =~ m/$var1/);
$res2 = ($matchStr =~ m/$var2/);

The $res2 statement complains that Unmatched ( before HERE mark in regex m.

Answer 1

Double quotes use variable expansion. Single quotes don't

In a double quoted string you need to escape certain characters to stop them being interpreted differently. In a single quoted string you don't (except for a backslash if it is the final character in the string)

my $var1 = 'Hello';

my $var2 = "$var1";
my $var3 = '$var1';

print $var2;
print "
";
print $var3;
print "
";

This will output

Hello
$var1

Perl Monks has a pretty good explanation of this here