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 quotation marks interpret, and single quotation do not

Answer 2

' will not resolve variables and escapes

" will resolve variables, and escape characters.

If you want to store your \ character in the string in $var2, use "\\("

Answer 3

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 "\n";
print $var3;
print "\n";

This will output

Hello
$var1

Perl Monks has a pretty good explanation of this here

Answer 4

"" Supports variable interpolation and escaping. so inside "\(" \ escapes (

Where as ' ' does not support either. So '\(' is literally \(

Answer 5

Perl takes the single-quoted strings 'as is' and interpolates the double-quoted strings. Interpolate means, that it substitutes variables with variable values, and also understands escaped characters. So, your "\(" is interpreted as '(', and your regexp becomes m/(/, this is why Perl complains.

Answer 6

If you are going to create regex strings you should really be using the qr// quote-like operator:

my $matchStr = "(";
my $var1 = qr/\(/;
my $res1 = ($matchStr =~ m/$var1/);

It creates a compiled regex that is much faster than just using a variable containing string. It also will return a string if not used in a regex context, so you can say things like

print "$var1\n"; #prints (?-xism:\()