If you use "" with eval, make sure you escape the $ in '$user_text'; otherwise, it'll be interpolated into a constant string.

sub do_it{
  #...
  eval "\$user_text =~ $regex";
  if (length $@){
    print "Error : $@";
  }else{
    print "User text: $user_text\n"
  }
  #...
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--perlplexer