Jun 1, 2017 · Specifically when does ^ mean "match start" and when does it mean "not the following" in regular expressions? From the Wikipedia article and other references, I've …

Oct 15, 2009 · May I know what ?= means in a regular expression? For example, what is its significance in this expression: (?=.*\\d).

Dec 8, 2018 · The regex compiles fine, and there are already JUnit tests that show how it works. It's just that I'm a bit confused about why the first question mark and colon are there.

Nov 30, 2011 · In case it is JS it indicates the start and end of the regex, like quotes for strings. stackoverflow.com/questions/15661969/…

I am using a regex to program an input validator for a text box where I only want alphabetical characters. I was wondering if [A-z] and [a-zA-Z] were equivalent or if there were differences …

The regex [a-z] will match any letter a through z. The () construct is a grouping construct establishing a precedence order (it also has impact on accessing matched substrings but …

Oct 3, 2010 · Now, when the regex engine tries to match against aaaaaaaab, the .* will again consume the entire string. However, since the engine will have reached the end of the string …

By putting ^ at the beginning of your regex and $ at the end, you ensure that no other characters are allowed before or after your regex. For example, the regex [0-9] matches the strings "9" as …

May 14, 2019 · I need a regex which will allow only A-Z, a-z, 0-9, the _ character, and dot (.) in the input. I tried: [A-Za-z0-9_.] But, it did not work. How can I fix it?

While writing this answer, I had to match exclusively on linebreaks instead of using the s-flag (dotall - dot matches linebreaks). The sites usually used to test regular expressions behave …