Initial CLI implementation

README.md

@@ -23,7 +23,7 @@ To start using GJSON, install Go and run `go get`:
 $ go get -u github.com/tidwall/gjson
 ```
 
-This will retrieve the library.
+This will retrieve the library. [You can also use GJSON as a CLI.](#use-as-cli)
 
 ## Get a value
 Get searches json for the specified path. A path is in dot syntax, such as "name.last" or "age". This function expects that the json is well-formed. Bad json will not panic, but it may return back unexpected results. When the value is found it's returned immediately. 
@@ -409,6 +409,66 @@ widget.text.size
 
 *These benchmarks were run on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.8.*
 
+## Use as CLI
+
+### Installation
+
+```sh
+$ go get -u github.com/tidwall/gjson/...
+$ which gjson
+$GOPATH/bin/gjson
+```
+
+### Usage
+
+View the help dialogue with the `-help` flag.
+
+```sh
+$ gjson -help
+usage: gjson [options] [path ...]
+  -in string
+      read JSON data from this file instead of stdin
+  -incl-path
+      include paths in output
+  -out string
+      write result to this file instead of stdout
+  -version
+      print version and exit
+```
+
+By default, GJSON reads from stdin and writes to stdout. Use the `-in` / `-out` flags to specify files to read to / write from. Note that GJSON **overwrites** the contents of `-out` (and creates the file if it doesn't exist yet).
+
+GJSON expects one or more paths as command line arguments. A path with escaped characters should be wrapped in quotes.
+
+### Examples
+
+```sh
+$ echo '{"name":{"first":"Janet","last":"Prichard"},"age":47}' | gjson name.last
+Prichard
+```
+
+The following examples use the JSON data from [this section](#path-syntax).
+
+```sh
+$ gjson name.last < data.json
+Anderson
+```
+
+```sh
+$ gjson name.last age "fav\.movie" < data.json > out
+$ cat out
+Anderson
+37
+Deer Hunter
+```
+
+```sh
+$ gjson -in data.json -out out -include-path children children.#
+$ cat out
+"children" : ["Sara","Alex","Jack"]
+"children.#" : 3
+```
+
 ## Contact
 Josh Baker [@tidwall](http://twitter.com/tidwall)
 

cmd/gjson/gjson.go

@@ -0,0 +1,98 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+
+	"github.com/tidwall/gjson"
+)
+
+const version = "0.0.1"
+
+var options struct {
+	in          string
+	out         string
+	includePath bool
+	version     bool
+}
+
+func readInput() ([]byte, error) {
+	if len(options.in) > 0 {
+		return ioutil.ReadFile(options.in)
+	}
+
+	// Check that stdin is not empty.
+	stat, err := os.Stdin.Stat()
+	if err != nil {
+		return []byte{}, err
+	}
+	if (stat.Mode() & os.ModeCharDevice) != 0 {
+		return []byte{}, errors.New("expected JSON data from stdin (run gjson -help)")
+	}
+
+	return ioutil.ReadAll(os.Stdin)
+}
+
+func printOutput(results []gjson.Result) error {
+	var (
+		out *os.File
+		err error
+	)
+
+	if len(options.out) > 0 {
+		out, err = os.Create(options.out)
+		if err != nil {
+			return err
+		}
+		defer out.Close()
+	} else {
+		out = os.Stdout
+	}
+
+	for i, result := range results {
+		if options.includePath {
+			fmt.Fprintf(out, "\"%s\" : ", flag.Args()[i])
+		}
+		fmt.Fprintln(out, result)
+	}
+
+	return nil
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "usage: %s [options] [path ...]\n", os.Args[0])
+		flag.PrintDefaults()
+	}
+
+	flag.StringVar(&options.in, "in", "", "read JSON data from this file instead of stdin")
+	flag.StringVar(&options.out, "out", "", "write result to this file instead of stdout")
+	flag.BoolVar(&options.includePath, "include-path", false, "include paths in output")
+	flag.BoolVar(&options.version, "version", false, "print version and exit")
+	flag.Parse()
+
+	if options.version {
+		fmt.Printf("gjson v%v\n", version)
+		os.Exit(0)
+	}
+
+	if len(flag.Args()) == 0 {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	bytes, err := readInput()
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+
+	results := gjson.GetMany(string(bytes), flag.Args()...)
+	err = printOutput(results)
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+}