/bb|[^b]{2}/ how does it work?
Assuming # for comments:
Regex
Find the location of a character in string
You can use gregexpr or perhaps str_locate_all from package stringr which is a wrapper for gregexpr stringi::stri_locate_all (as of stringr version 1.0) note that you could simply use stringi Another option in base R would be something like should work (given a character vector x)
Regular expression to stop at first match
You need to make your regular expression lazy/non-greedy, because by default, “(.*)” will match all of “file path/level1/level2″ xxx some=”xxx”. Instead you can make your dot-star non-greedy, which will make it match as few characters as possible: Adding a ? on a quantifier (?, * or +) makes it non-greedy. Note: this is only available … Read more
Regular expression – starting and ending with a character string
This should do it for you ^wp.*php$ Matches Doesn’t match
python regular expression “\1”
\1 is equivalent to re.search(…).group(1), the first parentheses-delimited expression inside of the regex. It’s also, fun fact, part of the reason that regular expressions are significantly slower in Python and other programming languages than required to be by CS theory.ShareFollowansw
Regex credit card number tests
Remove all , and – and other non-digits from the string first. Then use this regex that matches Visa, MasterCard, American Express, Diners Club, Discover, and JCB cards: ^(?:4[0-9]{12}(?:[0-9]{3})?|[25][1-7][0-9]{14}|6(?:011|5[0-9][0-9])[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|(?:2131|1800|35\d{3})\d{11})$
Regex: matching up to the first occurrence of a character
You need The [^;] is a character class, it matches everything but a semicolon. To cite the perlre manpage: You can specify a character class, by enclosing a list of characters in [] , which will match any character from the list. If the first character after the “[” is “^”, the class matches any character not in the list. … Read more
Regular expression for a string that does not start with a sequence
You could use a negative look-ahead assertion: Or a negative look-behind assertion: Or just plain old character sets and alternations:
How to ignore whitespace in a regular expression subject string?
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/
Regular expressions in C: examples?
Regular expressions actually aren’t part of ANSI C. It sounds like you might be talking about the POSIX regular expression library, which comes with most (all?) *nixes. Here’s an example of using POSIX regexes in C (based on this): Alternatively, you may want to check out PCRE, a library for Perl-compatible regular expressions in C. The Perl … Read more