In Operators§

See primary documentation in context for prefix ++

multi sub prefix:<++>($x is rw) is assoc<non>

Increments its argument by one and returns the updated value.

my $x = 3;
say ++$x;   # OUTPUT: «4␤» 
say $x;     # OUTPUT: «4␤»

It works by calling the succ method (for successor) on its argument, which gives custom types the freedom to implement their own increment semantics.

In Operators§

See primary documentation in context for postfix ++

multi sub postfix:<++>($x is rw) is assoc<non>

Increments its argument by one and returns the original value.

my $x = 3;
say $x++;   # OUTPUT: «3␤» 
say $x;     # OUTPUT: «4␤»

It works by calling the succ method (for successor) on its argument, which gives custom types the freedom to implement their own increment semantics; when undefined, it sets the value to 1 and returns it.

my $x;
$x++;
say $x;     # OUTPUT: «1␤»

Note that this does not necessarily return its argument; e.g., for undefined values, it returns 0:

my $x;
say $x++;   # OUTPUT: «0␤» 
say $x;     # OUTPUT: «1␤»

Increment on Str will increment the number part of a string and assign the resulting string to the container. An is rw container is required.

my $filename = "somefile-001.txt";
say $filename++ for 1..3;
# OUTPUT: «somefile-001.txt␤somefile-002.txt␤somefile-003.txt␤»

This will act on any Unicode numeral:

my $was٧ = "ثمانية٧";
$was٧++;
say $was٧; # OUTPUT: «ثمانية٨␤» 

Including, since version 6.d, Thai numerals

my $เลขไทย="๙๙";
$เลขไทย++;
say $เลขไทย; # OUTPUT: «๑๐๐␤»