#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $AoH_orig = [ { 'title' => 'aaa-aaa',
                   'name'  => 'tom' },
                 { 'title' => 'bbb-bbb',
                   'name'  => 'kathy' },
                 { 'title' => 'ccc-ccc',
                   'name'  => 'bill' }
                 ];

#try mapping
print Dumper ($AoH_orig);

my $AoH_new = map { $_->{'title'} =~ s/-/_/g } @$AoH_orig;

print Dumper($AoH_orig);
[download]

$VAR1 = [
          {
            'name' => 'tom',
            'title' => 'aaa-aaa'
          },
          {
            'name' => 'kathy',
            'title' => 'bbb-bbb'
          },
          {
            'name' => 'bill',
            'title' => 'ccc-ccc'
          }
        ];
$VAR1 = [
          {
            'name' => 'tom',
            'title' => 'aaa_aaa'
          },
          {
            'name' => 'kathy',
            'title' => 'bbb_bbb'
          },
          {
            'name' => 'bill',
            'title' => 'ccc_ccc'
          }
        ];
[download]

All dashes (-) are replaced with underscore (_) isn't that what you are trying?

I probably will not use map for this as you are not returning a list back. I would stick with your for for idea.

 $_->{'title'} =~ s/-/_/g for(@$AoH_orig); should work just fine (i think)

cheers

SK