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\",

Answer 1

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.