Four usages of regular expression question mark--Regular expression

Original symbol

Because there is a special meaning in the regular expression, so if you want to match it, you need to escape, \?

There are no quantifiers

A question mark can indicate that you repeat the previous content 0 or one time, that is either not present or occurs once.

Non-greedy match

Greedy match

Matches the string as long as possible when matching matches, by default, with greedy matching

String pattern1 = @ "A.*c";  Greedy match 
regex regex = new Regex (PATTERN1);
Regex. Match ("Abcabc"); Return "ABCABC"

Non-greedy match

Matches as short as possible when matching matches, using? to indicate non-greedy matches

String pattern1 = @ "A.*?c";  Non-greedy match 
regex regex = new Regex (PATTERN1);
Regex. Match ("Abcabc"); Return "ABC"

Several commonly used non-greedy matching pattern

*? Repeat any time, but try to repeat as little as possible
+? Repeat 1 or more times, but repeat as little as possible
?? Repeat 0 or 1 times, but repeat as little as possible
{n,m}? Repeat N to M times, but repeat as little as possible
{N,}? Repeat more than n times, but repeat as little as possible

Do not capture mode

How do I turn off the ability to capture parentheses? Instead of using it to group, the method is to add the following in the left parenthesis:?, where the first parenthesis is used for grouping only, not capturing the variable, so the contents can only be steak or burger, and can never be bronto.

while (<>) {
  if (/?: Bronto) (Steak|burger)/) {
    print "Fred wants a $1\n";
  }
}