What is the syntax to dereference a reference in Perl?
Whenever you can use the name of a variable, you can use a block that evaluates to a reference instead. For example, the following are valid syntax for specifying an array:
@NAME # If you have the name e.g. @array
@BLOCK # If you have a reference e.g. @{ $ref }
This is the "circumfix syntax" illustrated in the table below.
An alternative syntax colloquially known as the "arrow notation" is easier to read, but requires Perl 5.20+ in some cases. This is the "postfix syntax" illustrated in the table below.
Direct Using References Using References
Circumfix Syntax[1] Postfix Syntax
scalar itself $s ${$sr} $sr->$* [3]
array itself @a @{$ar} $ar->@* [3]
array element $a[0] ${$ar}[0] $ar->[0]
array slice @a[0,1,2] @{$ar}[0,1,2] $ar->@[0,1,2] [3]
array index-value slice[2] %a[0,1,2] %{$ar}[0,1,2] $ar->%[0,1,2] [3]
array last index $#a $#{$ar} $ar->$#* [3]
hash itself %h %{$hr} $hr->%* [3]
hash element $h{'a'} ${$hr}{'a'} $hr->{'a'}
hash slice @h{'a','b','c'} @{$hr}{'a','b','c'} $hr->@{'a','b','c'} [3]
hash key-value slice[2] %h{'a','b','c'} %{$hr}{'a','b','c'} $hr->%{'a','b','c'} [3]
code call func(@args)
code w/ ignored prototype &func(@args) &{$cr}(@args) $cr->(@args)
code w/ inherited @_ &func &{$cr} $cr->&* [3]
glob itself *glob *{$gr} $gr->** [3]
glob slot *glob{ARRAY} *{$gr}{ARRAY} $gr->*{ARRAY} [3]
Notes:
The curly brackets around $sr, $ar, $hr, $cr and $gr are optional when the contents of the curlies is simply a scalar variable.
If they are used, those curlies form blocks, so they can actually contain multiple statements.
Requires Perl 5.20+.
Requires Perl 5.24+. Available in Perl 5.20+ by adding both use feature qw( postderef ); and no warnings qw( experimental::postderef );, or by adding use experimental qw( postderef );. This is safe because the then-experimental feature was accepted into Perl without change.
See also: