How can I convert from underscores to camel case with a regex?

Question

Some Perl examples:

my $str = 'variable_name, VARIABLE_NAME, _var_x_short,  __variable__name___';

### solution 1
$_ = $str;

$_ = lc;
s/_(\w)/\U$1/g;

say;

### solution 2: multi/leading underscore fix
$_ = $str;

$_ = lc;
s/(?<=[^\W_])_+([^\W_])|_+/\U$1/g;

say;

### solution 3: without prior lc
$_ = $str;

s/(?<=[^\W_])_+([^\W_])|([^\W_]+)|_+/\U$1\L$2/g;

say;

Output:

variableName, variableName, VarXShort,  _variable_name__
variableName, variableName, varXShort,  variableName
variableName, variableName, varXShort,  variableName

Uppercases letters following _-:

s/[_-]([a-z])/\u$1/gr

If you already have camelCase variables in the string, then @Qtax's answer will make them lowercase. If all of your variables are lower-case under_scored then you can make the following modification to #3: W --> A-Z

's/(?<=[^\A-Z_])_+([^\A-Z_])|([^\A-Z_]+)|_+/\U$1\L$2/g'

I prefer user846969's answer but somehow it was not finding other matches in the tool that is using EBNF (extended Backus-Naur form). Here is somthing that worked for me:

/(?:([a-z0-9]*)[_-])([a-z])/${1}${2:/upcase}/g