adding regex support

README.md

@@ -63,6 +63,9 @@ To access an array value use the index as the key.
 To get the number of elements in an array or to access a child path, use the '#' character.
 The dot and wildcard characters can be escaped with '\\'.
 
+A path key can also be a valid regular expression. Provide the regular expression string by enclosing it '~'.
+If provided regular expression is valid, then it will return the matched result set. If regular expression is invalid, then we return an empty result set.
+
 ```json
 {
   "name": {"first": "Tom", "last": "Anderson"},
@@ -77,16 +80,19 @@ The dot and wildcard characters can be escaped with '\\'.
 }
 ```
 ```
-"name.last"          >> "Anderson"
-"age"                >> 37
-"children"           >> ["Sara","Alex","Jack"]
-"children.#"         >> 3
-"children.1"         >> "Alex"
-"child*.2"           >> "Jack"
-"c?ildren.0"         >> "Sara"
-"fav\.movie"         >> "Deer Hunter"
-"friends.#.first"    >> ["Dale","Roger","Jane"]
-"friends.1.last"     >> "Craig"
+"name.last"             >> "Anderson"
+"age"                   >> 37
+"children"              >> ["Sara","Alex","Jack"]
+"children.#"            >> 3
+"children.1"            >> "Alex"
+"child*.2"              >> "Jack"
+"c?ildren.0"            >> "Sara"
+"fav\.movie"            >> "Deer Hunter"
+"friends.#.first"       >> ["Dale","Roger","Jane"]
+"friends.1.last"        >> "Craig"
+"name.~\w~"             >> "Tom"
+"name.~la*~"            >> "Anderson"
+"friends.2.~^(\w{3})$~" >> 47
 ```
 
 You can also query an array for the first match by using `#(...)`, or find all 

SYNTAX.md

@@ -4,16 +4,21 @@ A GJSON Path is a text string syntax that describes a search pattern for quickly
 
 This document is designed to explain the structure of a GJSON Path through examples.
 
-- [Path structure](#path-structure)
-- [Basic](#basic)
-- [Wildcards](#wildcards)
-- [Escape Character](#escape-character)
-- [Arrays](#arrays)
-- [Queries](#queries)
-- [Dot vs Pipe](#dot-vs-pipe)
-- [Modifiers](#modifiers)
-- [Multipaths](#multipaths)
-- [Literals](#literals)
+- [GJSON Path Syntax](#gjson-path-syntax)
+  - [Path structure](#path-structure)
+  - [Example](#example)
+    - [Basic](#basic)
+    - [Wildcards](#wildcards)
+    - [Regular Expression](#regular-expression)
+    - [Escape character](#escape-character)
+    - [Arrays](#arrays)
+    - [Queries](#queries)
+    - [Dot vs Pipe](#dot-vs-pipe)
+    - [Modifiers](#modifiers)
+      - [Modifier arguments](#modifier-arguments)
+      - [Custom modifiers](#custom-modifiers)
+    - [Multipaths](#multipaths)
+    - [Literals](#literals)
 
 The definitive implemenation is [github.com/tidwall/gjson](https://github.com/tidwall/gjson).  
 Use the [GJSON Playground](https://gjson.dev) to experiment with the syntax online.
@@ -69,6 +74,15 @@ child*.2               "Jack"
 c?ildren.0             "Sara"
 ```
 
+### Regular Expression
+Regular expression based key matching is supported, but the expression should be enclosed by `~`. If the provided regular expression is invalid, then it always return empty result set.
+
+```go
+~fav.*~               "Deer Hunter"
+friends.#.~fir*~      ["Dale","Roger","Jane"]
+~[~
+```
+
 ### Escape character
 
 Special purpose characters, such as `.`, `*`, and `?` can be escaped with `\`. 

gjson.go

@@ -3,6 +3,7 @@ package gjson
 
 import (
 	"encoding/json"
+	"regexp"
 	"strconv"
 	"strings"
 	"time"
@@ -943,17 +944,19 @@ type objectPathResult struct {
 	piped bool
 	wild  bool
 	more  bool
+	regex bool
 }
 
 func parseObjectPath(path string) (r objectPathResult) {
+	var regexBegin = false
 	for i := 0; i < len(path); i++ {
 		if path[i] == '|' {
 			r.part = path[:i]
 			r.pipe = path[i+1:]
 			r.piped = true
 			return
 		}
-		if path[i] == '.' {
+		if path[i] == '.' && !regexBegin {
 			r.part = path[:i]
 			if i < len(path)-1 && isDotPiperChar(path[i+1]) {
 				r.pipe = path[i+1:]
@@ -968,7 +971,17 @@ func parseObjectPath(path string) (r objectPathResult) {
 			r.wild = true
 			continue
 		}
-		if path[i] == '\\' {
+		if path[i] == '~' {
+
+			if !regexBegin {
+				regexBegin = true
+			} else {
+				r.regex = true
+				regexBegin = false
+			}
+			continue
+		}
+		if path[i] == '\\' && !regexBegin {
 			// go into escape mode. this is a slower path that
 			// strips off the escape character from the part.
 			epart := []byte(path[:i])
@@ -1123,17 +1136,26 @@ func parseObject(c *parseContext, i int, path string) (int, bool) {
 		if !ok {
 			return i, false
 		}
-		if rp.wild {
+
+		if rp.regex {
 			if kesc {
-				pmatch = matchLimit(unescape(key), rp.part)
+				pmatch = matchRegex(unescape(key), rp.part)
 			} else {
-				pmatch = matchLimit(key, rp.part)
+				pmatch = matchRegex(key, rp.part)
 			}
 		} else {
-			if kesc {
-				pmatch = rp.part == unescape(key)
+			if rp.wild {
+				if kesc {
+					pmatch = matchLimit(unescape(key), rp.part)
+				} else {
+					pmatch = matchLimit(key, rp.part)
+				}
 			} else {
-				pmatch = rp.part == key
+				if kesc {
+					pmatch = rp.part == unescape(key)
+				} else {
+					pmatch = rp.part == key
+				}
 			}
 		}
 		hit = pmatch && !rp.more
@@ -1232,6 +1254,18 @@ func matchLimit(str, pattern string) bool {
 	return matched
 }
 
+func matchRegex(str, pattern string) bool {
+	// Remove the enclosed pattern character "~"
+	match, err := regexp.MatchString(strings.Trim(pattern, "~"), str)
+	if err != nil {
+		// XXX
+		// If regex is invalid, then do not throw any error.
+		// Rather, return false to the calling environment.
+		return false
+	}
+	return match
+}
+
 func queryMatches(rp *arrayPathResult, value Result) bool {
 	rpv := rp.query.value
 	if len(rpv) > 0 && rpv[0] == '~' {

gjson_test.go

@@ -105,6 +105,10 @@ func TestEscapePath(t *testing.T) {
 	testEscapePath(t, json, "test.keyv\\.", "val5")
 	testEscapePath(t, json, "test.key\\.v", "val6")
 	testEscapePath(t, json, "test.keyk\\*.key\\?", "val7")
+
+	//XXX
+	//Do we have escaped regex string as key ?
+	//Rather, let user provide a valid regex to perform the escape.
 }
 
 // this json block is poorly formed on purpose.
@@ -200,6 +204,27 @@ func TestPath(t *testing.T) {
 	get("lastly.end\\.\\.\\.ing")
 	get("lastly.yay")
 
+	//XXX
+	//Regex path testing goes here
+	regexGet := func(path string, isValid bool) {
+		r1 := Get(json, path)
+		if isValid {
+			assert(t, r1.Raw != "")
+		} else {
+			assert(t, r1.Raw == "")
+		}
+	}
+
+	//XXX
+	//Testing a valid regular expression path
+	regexGet("~.~", true)
+	regexGet("loggy.~programmers~", true)
+	regexGet("~last*~.~end*~", true)
+	//Get any 3 word length string from the JSON path
+	regexGet(`loggy.programmers.2.~^(\w{3})$~`, true)
+
+	//Testing an invalid regular expression
+	regexGet("~[0-9~", false)
 }
 
 func TestTimeResult(t *testing.T) {