ilham76c · July 15, 2023 17:19 · Jul 15, 2023 · Jul 15, 2023
diff --git a/gistfile1.txt → regex.md b/gistfile1.txt → regex.md
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,46 @@
+## Definitions
+
+## Look ahead positive `(?=)`
+
+Find expression A where expression B follows:
+
+```plaintext
+A(?=B)
+```
+
+## Look ahead negative `(?!)`
+
+Find expression A where expression B does not follow:
+
+```plaintext
+A(?!B)
+```
+
+## Look behind positive `(?<=)`
+
+Find expression A where expression B precedes:
+
+```plaintext
+(?<=B)A
+```
+
+## Look behind negative `(?<!)`
+
+Find expression A where expression B does not precede:
+
+```plaintext
+(?<!B)A
+```
+
+## Atomic groups `(?>)`
+
+An atomic group exits a group and throws away alternative patterns after the _first_ matched pattern inside the group (backtracking is disabled).
+
+*   `(?>foo|foot)s` applied to `foots` will match its 1st alternative `foo`, then fail as `s` does not immediately follow, and stop as backtracking is disabled
+
+A non-atomic group will allow backtracking; if subsequent matching ahead fails, it will backtrack and use alternative patterns until a match for the entire expression is found or all possibilities are exhausted.
+
+`(foo|foot)s` applied to `foots` will:
+
+1.  match its 1st alternative `foo`, then fail as `s` does not immediately follow in `foots`, and backtrack to its 2nd alternative;
+2.  match its 2nd alternative `foot`, then succeed as `s` immediately follows in `foots`, and stop.
No results found