Interpolation in Perl

What is interpolated

Perl interpolates variable names:

my $name = 'Paul';
print "Hello, $name!\n"; # Hello, Paul!

my @char = ('a', 'b', 'c');
print "$char[1]\n"; # b

my %map = (a => 125, b => 1080, c => 11);
print "$map{a}\n"; # 125

Arrays may be interpolated as a whole, their elements are separated by spaces:

my @char = ('a', 'b', 'c');
print "My chars are @char\n"; # My chars are a b c

Perl does not interpolate hashes as a whole:

my %map = (a => 125, b => 1080, c => 11);
print "My map is %map\n"; # My map is %map

and function calls (including constants):

use constant {
    PI => '3.1415926'
};
print "I like PI\n";         # I like PI
print "I like " . PI . "\n"; # I like 3.1415926

Perl interpolates escape sequences starting with \:

\t                  horizontal tab
\n                  newline
\r                  return
\f                  form feed
\b                  backspace
\a                  alarm (bell)
\e                  escape

Interpolation of \n depends on the system where program is working: it will produce a newline character(s) according to the current system conventions.

Perl does not interpolate \v, which means vertical tab in C and other languages.

Character may be addressed using their codes:

\x{1d11e}     𝄞 by hexadecimal code
\o{350436}    𝄞 by octal code
\N{U+1d11e}   𝄞 by Unicode code point

or Unicode names:

\N{MUSICAL SYMBOL G CLEF}

Character with codes from 0x00 to 0xFF in the native encoding may be addressed in a shorter form:

\x0a     hexadecimal
\012     octal

Control character may be addressed using special escape sequences:

\c@      chr(0)
\ca      chr(1)
\cb      chr(2)
...
\cz      chr(26)
\c[      chr(27)
\c\      chr(28) # Cannot be used at the end of a string
                 # since backslash will interpolate the terminating quote
\c]      chr(29)
\c^      chr(30)
\c_      chr(31)
\c?      chr(127)

Uppercase letters have the same meaning: "\cA" == "\ca".

Interpretation of all escape sequences except for \N{...} may depend on the platform since they use platform- and encoding-dependent codes.

Basic interpolation

Interpolation means that Perl interpreter will substitute the values of variables for their name and some symbols (which are impossible or difficult to type in directly) for special sequences of characters (it is also known as escaping). The most important distinction is between single and double quotes: double quotes interpolate the enclosed string, but single quotes do not.

my $name = 'Paul';
my $age = 64;
print "My name is $name.\nI am $age.\n"; # My name is Paul.
                                         # I am 64.

But:

print 'My name is $name.\nI am $age.\n'; # My name is $name.\nI am $age.\n

You can use q{} (with any delimiter) instead of single quotes and qq{} instead of double quotes. For example, q{I'm 64} allows to use an apostrophe within a non-interpolated string (otherwise it would terminate the string).

Statements:

print qq{$name said: "I'm $age".}; # Paul said: "I'm 64".
print "$name said: \"I'm $age\"."  # Paul said: "I'm 64".

do the same thing, but in the first one you do not need to escape double quotes within the string.

If your variable name clashes with surrounding text, you can use the syntax ${var} to disambiguate:

my $decade = 80;
print "I like ${decade}s music!"  # I like 80s music!