init

regex.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+echo '
+Character classes
+  . any character except newline
+  \w \d \s  word, digit, whitespace
+  \W \D \S  not word, digit, whitespace
+  [abc] any of a, b, or c
+  [^abc]  not a, b, or c
+  [a-g] character between a & g
+Anchors
+  ^abc$ start / end of the string
+  \\b \\B word, not-word boundary
+Escaped characters
+  \. \* \\  escaped special characters
+  \\t \\n \\r  tab, linefeed, carriage return
+  \u00A9  unicode escaped ©
+Groups and Lookaround
+  (abc) capture group
+  \\1  backreference to group #1
+  (?:abc) non-capturing group
+  (?=abc) positive lookahead
+  (?!abc) negative lookahead
+Quantifiers & Alternation
+  a* a+ a?  0 or more, 1 or more, 0 or 1
+  a{5} a{2,}  exactly five, two or more
+  a{1,3}  between one & three
+  a+? a{2,}?  match as few as possible
+  ab|cd match ab or cd
+'