Set a sensible default for -cache.

Change-Id: I91c11935545df034beae9bd3e0eaf073c4660e75

cmd/gitfs-gitilesfs/main.go

diff --git a/cmd/gitfs-gitilesfs/main.go b/cmd/gitfs-gitilesfs/main.go
index 8fbd9eb..078a1a0 100644
--- a/cmd/gitfs-gitilesfs/main.go
+++ b/cmd/gitfs-gitilesfs/main.go
@@ -17,6 +17,8 @@
 import (
 	"flag"
 	"log"
+	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/google/gitfs/cache"
@@ -30,7 +32,7 @@
 	branch := flag.String("branch", "master", "branch name")
 	repo := flag.String("repo", "", "repository name")
 	debug := flag.Bool("debug", false, "print debug info")
-	cacheDir := flag.String("cache", "", "cache dir")
+	cacheDir := flag.String("cache", filepath.Join(os.Getenv("HOME"), ".cache", "gitfs"), "cache dir")
 	flag.Parse()
 
 	if *cacheDir == "" {

cmd/gitfs-manifestfs/main.go

diff --git a/cmd/gitfs-manifestfs/main.go b/cmd/gitfs-manifestfs/main.go
index e7ce6ba..a02ab22 100644
--- a/cmd/gitfs-manifestfs/main.go
+++ b/cmd/gitfs-manifestfs/main.go
@@ -16,7 +16,10 @@
 
 import (
 	"flag"
+	"io/ioutil"
 	"log"
+	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/google/gitfs/cache"
@@ -29,7 +32,7 @@
 func main() {
 	manifestPath := flag.String("manifest", "", "expanded manifest file path")
 	gitilesURL := flag.String("gitiles", "", "gitiles URL. If unset, derive from manifest location.")
-	cacheDir := flag.String("cache", "", "cache dir")
+	cacheDir := flag.String("cache", filepath.Join(os.Getenv("HOME"), ".cache", "gitfs"), "cache dir")
 	debug := flag.Bool("debug", false, "print debug info")
 	config := flag.String("config", "", "JSON file configuring what repositories should be cloned.")
 	flag.Parse()

cmd/gitfs-multifs/main.go

diff --git a/cmd/gitfs-multifs/main.go b/cmd/gitfs-multifs/main.go
index 7d4b1ef..23d9c48 100644
--- a/cmd/gitfs-multifs/main.go
+++ b/cmd/gitfs-multifs/main.go
@@ -18,6 +18,8 @@
 	"flag"
 	"io/ioutil"
 	"log"
+	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/google/gitfs/cache"
@@ -28,7 +30,7 @@
 
 func main() {
 	gitilesURL := flag.String("gitiles", "", "gitiles URL. If unset, derive from manifest location.")
-	cacheDir := flag.String("cache", "", "cache dir")
+	cacheDir := flag.String("cache", filepath.Join(os.Getenv("HOME"), ".cache", "gitfs"), "cache dir")
 	debug := flag.Bool("debug", false, "print debug info")
 	config := flag.String("config", "", "JSON file configuring what repositories should be cloned.")
 	flag.Parse()