How to ignore whitespace in a regular expression subject string

Question

Is there a simple way to ignore the white space in a target string when searching for matches using a regular expression pattern   For example  if my search is for  cats   I would want  c ats  or  ca   ts  to match   I can t strip out the whitespace beforehand because I need to find the begin and end index of the match  including any whitespace  in order to highlight that match and any whitespace needs to be there for formatting purposes

User · Answer

You could put  s  inbetween every character in your search string so if you were looking for cat you would use c s a s t s s s s  It s long but you could build the string dynamically of course   You can see it working here  http   www rubular com r zzWwvppSpE

User · Answer

You can stick optional whitespace characters  s  in between every other character in your regex   Although granted  it will get a bit lengthy    cats  -   c s a s t s s

User · Answer

While the accepted answer is technically correct  a more practical approach  if possible  is to just strip whitespace out of both the regular expression and the search string   If you want to search for  my cats   instead of   myString match  m s y s c s a  st s s s  g    Just do   myString replace   s  g     match  mycats g    Warning  You can t automate this on the regular expression by just replacing all spaces with empty strings because they may occur in a negation or otherwise make your regular expression invalid

User · Answer

Addressing Steven s comment to Sam Dufel s answer     Thanks  sounds like that s the way to go  But I just realized that I only want the optional whitespace characters if they follow a newline  So for example   c n ats  or  ca n ts  should match  But wouldn t want  c ats  to match if there is no newline  Any ideas on how that might be done    This should do the trick    c    n s   a    n s   t    n s   s    See this page for all the different variations of  cats  that this matches   You can also solve this using conditionals  but they are not supported in the javascript flavor of regex

User · Answer

If you only want to allow spaces  then   bc  a  t  s b   should do it  To also allow tabs  use   bc   t  a   t  t   t  s b   Remove the  b anchors if you also want to find cats within words like bobcats or catsup

User · Answer

This approach can be used to automate this  the following exemplary solution is in python  although obviously it can be ported to any language    you can strip the whitespace beforehand AND save the positions of non-whitespace characters so you can use them later to find out the matched string boundary positions in the original string like the following   def regex search ignore space regex  string       no spaces          char positions           for pos  char in enumerate string           if re match r  S   char      upper  S matches non-whitespace chars             no spaces    char             char positions append pos       match   re search regex  no spaces      if not match          return match        match start   and match end   are indices of start and end       of the found string in the spaceless string        as we have searched in it       start   char positions match start       in the original string     end   char positions match end       in the original string     matched string   string start end     see        the match WITH spaces is returned      return matched string  with spaces    a li on and a cat  print regex search ignore space  lion   with spaces     prints  li on    If you want to go further you can construct the match object and return it instead  so the use of this helper will be more handy   And the performance of this function can of course also be optimized  this example is just to show the path to a solution

[regex] How to ignore whitespace in a regular expression subject string?

Examples related to regex

Examples related to whitespace