defined vs exists:

sub foo {}
sub bar;

my @names = qw( foo bar baz );

local $, = "\t";
local $\ = "\n";
print('',                                  @names);
print('exists',  map { exists(&$_)  ?1:0 } @names);
print('defined', map { defined(&$_) ?1:0 } @names);
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        foo     bar     baz
exists  1       1       0
defined 1       0       0
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You can't call the ones that exist but aren't defined, so defined is probably a better choice.

>perl -e"sub bar; bar()"
Undefined subroutine &main::bar called at -e line 1.
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