1. Most regular expressions have their own flavor2. Perl matches the following expressions: $ variable = ~ m / regex / 3, the meaning of metamorphism depends on Context4, / T Tab / n newline / R Enter / Sleek character (space, tab, newline, etc.) / s non / S / W [A-ZA-Z0-9_] / W non-/ w / d [0-9] / d non-D / B head or Word tail 5, parameter i: case in case 6, (?: ...) Does not capture sub-expression 7, Perl uses $ 1, $ 2, $ 3, etc., represents the matched sub-expression. The child expression is numbered in the order of the left bracket. In addition to the explanation of 6, the remaining () is a captive sub-expression
