Try this more complete, corrected version of your code:

use strict;
use warnings;
my @h = (
  sub { return sprintf ("0x%x in HEX\n", shift) },
  sub { return sprintf ("%b in Binary\n", shift) },
  sub { return sprintf ("%d in Decimal\n", shift) },
);

print $_->(5) for @h;
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Now - an Explanation:

First, you need @h, not %h for an array .

Next, the "for" loop places each element of the array (which happens to be a "sub"routine reference, into $_.

THen The $_->() actually CALLS the subroutine (an anonomyous one). Each delcared anonymous subroutine is called in sequence

the constant "5" is passed in, separately to each call.

The "shift" actually does "shift @_", which retrieves the parameter (5).

You should read the documentation in perlsub.

Update:Here is how to use a hash for this structure properly:

use strict;
use warnings;
my %h = (
  HEX => sub { return sprintf ("0x%x ", shift) },
  BIN => sub { return sprintf ("%b", shift) },
  DEC => sub { return sprintf ("%d", shift) },
);

my $value = 5;

for my $fmt (sort keys %h){
  print "$value in $fmt is: ", $h{$fmt}->($value) , "\n";
}
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