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Editorial Team
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Asked: 2026-05-16T01:24:45+00:00

What’s happening behind the scenes when I do a concatenation on a string? my

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What’s happening behind the scenes when I do a concatenation on a string?

my $short = 'short';
$short .= 'cake';

Is Perl effectively creating a new string, then assigning it the correct variable reference, or are Perl strings always mutable by nature?

The motivation for this question came from a discussion I had with a colleague, who said that scripting languages can utilize immutable strings.

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1 Answer

  1. Editorial Team

    Perl strings are mutable. Perl automatically creates new buffers, if required.

    use Devel::Peek;
my $short = 'short';

Dump($short);
Dump($short .= 'cake');
Dump($short = "");

SV = PV(0x28403038) at 0x284766f4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x28459078 "short"\0
  CUR = 5
  LEN = 8
SV = PV(0x28403038) at 0x284766f4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x28458120 "shortcake"\0
  CUR = 9
  LEN = 12
SV = PV(0x28403038) at 0x284766f4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x28458120 ""\0
  CUR = 0
  LEN = 12

    Note that no new buffer is allocated in the third case.

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