alternation using pipe character
Backreferences to find the same text again
search and replace for chrome bookmarks clean up
class names in java and c#
lookahead and lookbehind
Negation and character classes
links:
regex cheatsheet (local .pdf)
regular-expressions.info tutorials
Regular-Expressions.info - great detailed tutorial
use \Q ... \E to treat any escape chars as string literals - a quantifier such as + after the \E repeats only the last character
Visual Studio regex table - use {} rather than Editpad's () to tag for replacement with \1 \2 etc
Microsoft reference for regex in .NET
short though incomplete summary
\b word boundary
\d digit
\w word character [A-Za-z0-9_] and potentially more depending on regex flavor
\s whitespace character
[ \t\r\n\f] and potentially more depending on regex flavor - note that \f is a form feed
\D not a digit = [^\d]
\W not a word character
\S not a whitespace character
? optional
the question mark for optional, the plus, the star and the repetition using curly braces are greedy; to make them lazy, append a question mark
this stackexchange post claims c# uses the same syntax as java and points to this post about regular expressions searching for java class names
| ahead | behind | |
|---|---|---|
| positive | (?=regex) | (?<=regex) |
| negative | (?!regex)
error(?!( - process|:.{0,1}\r\n|:\x0c)) error not immediately followed by any of these |
(?<!regex) |
| positive capture | (?=(regex)) | (?<=(regex)) |
| negavtive capture | (?!(regex)) | (?<!(regex)) |
e.g. to find newlines that don't have a preceding carriage return use negative lookbehind (?<!\r)\n
[] for a character class
[^] for a negated character class
^(.*?\,){4} .csv 4th item from start of line
(([^,\r\n]+),){3} 3 commas anywhere on a line except first position
e.g. finds lines that don't have var or if ^(?!.*(var|if).*\r\n)
\b(cat|dog)\b finds [word boundary] [then either cat or dog] [then word boundary] compared to \bcat|dog\b which finds either [word boundary then cat] or [dog then word boundary]
see this page
last updated: Thu 2023-03-09 5:43 AM