sub ucwords {
        join $_[1], map ucfirst lc, split /\Q$_[1]\E/, $_[0], -1;
    }
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To be called like:

    print ucwords("BATCH_USER_INFO", "_");
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Tsk tsk.

print ucwords("hello_world_", "_");
print ucwords("hello*world", "*");
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You need to specify the third argument to split and handle meta characters more carefully...

sub ucwords {
  (my $new = $_[0]) =~ s/(?<=$_[1])(\w)/\u$1/sg;
  return $new;
}
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japhy -- Perl and Regex Hacker

That's a nice solution, but but I think it is missing a couple features: it doesn't catch the first word in the string; it doesn't lowercase the rest of each word; and it doesn't allow variable-width delimiters. Here's a modified version that addresses those issues.

sub ucwords {
  my($new, $delim) = @_;
  $new =~ s/($delim|^)(.*?)(?=$delim|$)/$1\u\L$2/sg;
  $new;
}
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To match an entire word, from one delimiter to the next, I used a non-greedy match and a positive lookahead.

That's slick but it doesn't quite work:

    print ucwords("BATCH_USER_INFO", "_"), "\n";
    print ucwords("batch_user_info", "_"), "\n";
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produces

    BATCH_USER_INFO
    batch_User_Info
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In the first case you don't ever lower-case the string; in the second case you don't look for "word" at the beginning of the string, before the delim.