Adds usage function.

Author: Mariano Gappa

main.go

@@ -25,39 +25,39 @@ type database struct {
 func main() {
 	usr, err := user.Current()
 	if err != nil {
-		log.Fatalf("Couldn't obtain the current user err=%v", err)
+		usage("Couldn't obtain the current user err=%v", err)
 	}
 
 	databasesFile := usr.HomeDir + "/.databases.json"
 	databases := map[string]database{}
 
 	byts, err := ioutil.ReadFile(databasesFile)
 	if err != nil {
-		log.Fatalf("Couldn't read [%v] file. err=%v", databasesFile, err)
+		usage("Couldn't read [%v] file. err=%v", databasesFile, err)
 	}
 
 	err = json.Unmarshal(byts, &databases)
 	if err != nil {
-		log.Fatalf("Couldn't unmarshal [%v] file. err=%v", databasesFile, err)
+		usage("Couldn't unmarshal [%v] file. err=%v", databasesFile, err)
 	}
 
 	if len(databases) == 0 {
-		log.Fatalf("Couldn't find any database configurations in [%v] file.", databasesFile)
+		usage("Couldn't find any database configurations in [%v] file.", databasesFile)
 	}
 
 	sql := readInput(os.Stdin)
 	if len(sql) <= 3 {
-		log.Fatal("No SQL to run. Exiting.")
+		usage("No SQL to run. Exiting.")
 	}
 
 	if len(os.Args[1:]) == 0 {
-		log.Fatal("Target database unspecified; where should I run the query?")
+		usage("Target database unspecified; where should I run the query?")
 	}
 
 	targetDatabases := []string{}
 	for _, k := range os.Args[1:] {
 		if _, ok := databases[k]; k != "all" && !ok {
-			log.Fatalf("Target database unknown: [%v]", k)
+			usage("Target database unknown: [%v]", k)
 		}
 		if k == "all" {
 			targetDatabases = nil

usage.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func usage(error string, args ...interface{}) {
+	if len(error) > 0 {
+		if len(args) > 0 {
+			fmt.Println(fmt.Sprintf(error, args))
+		} else {
+			fmt.Println(error)
+		}
+		fmt.Println()
+	}
+
+	fmt.Println(`usage: ... | sql target_1 [target_2 ...]
+
+e.g.
+
+  cat query.sql | sql test_db
+
+  sed 's/2015/2016/g' query_for_2015.sql | sql db1 db2 db3
+
+  echo "SELECT * FROM users WHERE name = 'John'" | sql all
+
+For more detailed help, please go to: https://github.com/MarianoGappa/sql
+`)
+	os.Exit(1)
+}