Double Quoted Strings

Perl
Syntax
string
here

A double-quoted string is a string enclosed in double-quote. In Double quote string, Variable expansions and escape sequences can be used.

my $name = "Yuki Kimoto";

# Use variable expansion and line break characters
my $message = "I'm $name\n";

# "I'm Yuki Kimoto" is displayed. With a line break
print $message;

What is variable expansion?

Variable expansion is a function that allows you to expand the contents of a variable in a string.

my $name = "Yuki Kimoto";

# Use variable expansion and line break characters
my $message = "I'm $name\n";

If you want to clarify the delimiter of the variable name, you can specify it by enclosing the variable name excluding the sigil "$" with "{}".

my $name = "Yuki Kimoto";

# Specify variable name
my $message = "I'm ${name} _foo\n";

Details are explained in the article on variable expansion.

Variable expansion

Escape sequence of double quoted strings

Here are the escape sequences that can be used in double-quoted strings.

Frequently used ones are a line break "\n", tabs "\t", double quotes "\" ", and backslashes themselves" \\ ".

Escape sequence	Meaning
\n	Line breaks
\t	tab
\"	"
\\	\

Some escape sequences allow you to write the ASCII code itself by starting with "\x".

# Specify ASCII code directly to express a line break
my $message = "Hello\x0D\x0A";
print $message;

The above example is an example that expresses the line feed code in the HTTP protocol because it is an ASCII hexadecimal sequence of "D" and "A". The 0 after the "\x" is not required, but it is included according to the convention of representing ASCII codes in 2-digit hexadecimal numbers.

You can read more about it in the Double Quote String Escape Sequence article.

Double quote string escape sequence

Relationship with regular expression literals

Variable expansion and escape sequences of double-quoted strings can be used as they are in regular expression literals.

my $name = "Yuki Kimoto";

my $message = "I'm Yuki Kimoto\tHello";

# You can use variable expansion and escape sequences in regular expression literals
if ($message =~ /$name\t/) {
  
}

One of the reasons Perl's text processing is useful is that you can use double-quoted string interpolation and escape sequences as-is in regular expression literals.

I don't use variable expansion very often, but I feel that the fact that regular expression literals are a natural extension of double-quoted strings is a natural experience.

In Perl, regular expression are built in as programming language features, and regular expression literals are also implemented as one of the language features.

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