Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
local($x) saves away the old value of the global variable $x
, and assigns a new value for the duration of the subroutine, which is
visible in other functions called from that subroutine. This is done at run-time, so is called dynamic scoping.
local()
always affects global
variables, also called package variables or dynamic variables.
my($x) creates a new variable that is only visible in the current subroutine. This is done at compile-time, so is called lexical or static scoping.
my()
always affects private variables, also called lexical variables or (improperly)
static(ly
scoped) variables.
For instance:
sub visible { print "var has value $var "; }
sub dynamic { local $var = 'local'; # new temporary value for the still-global visible(); # variable called $var }
sub lexical { my $var = 'private'; # new private variable, $var visible(); # (invisible outside of sub scope) }
$var = 'global';
visible(); # prints global dynamic(); # prints local lexical(); # prints global
Notice how at no point does the value ``private'' get printed. That's because $var
only has that value within the block of the
lexical()
function, and it is hidden from called subroutine.
In summary,
local()
doesn't make what you think of as private, local variables. It gives a global variable a temporary value.
my()
is what you're looking for if you want private variables.
See Private Variables via my() and Temporary Values via local() for excruciating details.