Question

Need single regular expression for finding

1. double spaces
2. tabs
3. extra enter (line-break/carriage return)
4. line break between tag
5. space after/before closing tag

in an XML document.

Answer 1

In general you need an xml parser to process xml documents. Regular expressions are not powerful enough to handle all cases.

Using perl syntax for regexes:

m{
  [ ][ ]  # double spaces
  |
  \t    # tab
  |    
  $\s*$  # extra enter separated only by whitespace. Note: requires `m` flag
  |  
  # XXX: it works only on simple xml
  <[^<>]*$[^<>]*> # line break inside tag
  |
  # XXX: it works only on simple xml
  [ ]</[^<>]+> |
  </[^<>]+>[ ] # space after/before closing tag
}mxg;

demo