Regex: ?: notation (Question mark and colon notation) If efficiency were a consideration, would be better off coding the operation by hand instead of using regex's, rather than accept the efficiency gain of capturing vs non capturing groups IMO, the decision of whether to use capturing vs non capturing should simply document the intent of the expression
regex - Carets in Regular Expressions - Stack Overflow JavaScript caret in regex not working as expected Hot Network Questions Start collecting Social Security before Full retirement, what affect on calculating pct when switching to "half" spouse's when spouse starts?
meaning of dollar symbol in regular expression Let's deconstruct your regex (I removed the backslashes that are used to escape characters for the sake of simplification, we will use the dots and slashes as literal here) so we're left with : ^ means the beginning of a line
regex - Question marks in regular expressions - Stack Overflow Now, by default, the RegEx e will find the third letter e in word There There ^ However if you don't want the e which is immediately followed by r, then you can use RegEx e(?!r) Now the result would be: There ^ Positive Lookahead Positive lookahead works just the same
javascript - What is the need for caret (^) and dollar symbol ($) in . . . Fast regexen also need an "anchor" point, somewhere to start it's search somewhere in the string These characters tell the Regex engine where to start looking and generally reduce the number of backtracks, making your Regex much, much faster in many cases NOTE: This knowledge came from Nicolas Zakas's High Performance Javascript
regex - Dollar sign in regular expression and new line character . . . So, the String before the $ would of course not include the newline, and that is why ([A-Za-z ]+\n)$ regex of yours failed, and ([A-Za-z ]+)$\n succeeded In simple words, your $ should be followed by a newline, and no other character
regex - What is the difference between . *? and . * regular expressions . . . On greedy vs non-greedy Repetition in regex by default is greedy: they try to match as many reps as possible, and when this doesn't work and they have to backtrack, they try to match one fewer rep at a time, until a match of the whole pattern is found