3 files changed, 164 insertions, 3 deletions
diff --git a/cmd/utils/customflags.go b/cmd/utils/customflags.go
new file mode 100644
index 000000000..6d4a87bfb
--- /dev/null
+++ b/cmd/utils/customflags.go
@@ -0,0 +1,133 @@
+package utils
+import (
+    "path/filepath"
+    "os"
+    "strings"
+    "os/user"
+    "github.com/codegangsta/cli"
+    "flag"
+    "fmt"
+)
+
+// Custom type which is registered in the flags library which cli uses for
+// argument parsing. This allows us to expand Value to an absolute path when
+// the argument is parsed
+type DirectoryString struct {
+    Value string
+}
+
+func (self DirectoryString) String() string {
+    return self.Value
+}
+
+func (self DirectoryString) Set(value string) error {
+    self.Value = expandPath(value)
+    return nil
+}
+
+// Custom cli.Flag type which expand the received string to an absolute path.
+// e.g. ~/.ethereum -> /home/username/.ethereum
+type DirectoryFlag struct {
+    cli.GenericFlag
+    Name   string
+    Value  DirectoryString
+    Usage  string
+    EnvVar string
+}
+
+func (self DirectoryFlag) String() string {
+    var fmtString string
+    fmtString = "%s %v\t%v"
+
+    if len(self.Value.Value) > 0 {
+        fmtString = "%s \"%v\"\t%v"
+    } else {
+        fmtString = "%s %v\t%v"
+    }
+
+    return withEnvHint(self.EnvVar, fmt.Sprintf(fmtString, prefixedNames(self.Name), self.Value.Value, self.Usage))
+}
+
+func eachName(longName string, fn func(string)) {
+    parts := strings.Split(longName, ",")
+    for _, name := range parts {
+        name = strings.Trim(name, " ")
+        fn(name)
+    }
+}
+// called by cli library, grabs variable from environment (if in env)
+// and adds variable to flag set for parsing.
+func (self DirectoryFlag) Apply(set *flag.FlagSet) {
+    if self.EnvVar != "" {
+        for _, envVar := range strings.Split(self.EnvVar, ",") {
+            envVar = strings.TrimSpace(envVar)
+            if envVal := os.Getenv(envVar); envVal != "" {
+                self.Value.Value = envVal
+                break
+            }
+        }
+    }
+
+    eachName(self.Name, func(name string) {
+        set.Var(self.Value, self.Name, "a: " + self.Usage)
+    })
+
+}
+
+func prefixFor(name string) (prefix string) {
+    if len(name) == 1 {
+        prefix = "-"
+    } else {
+        prefix = "--"
+    }
+
+    return
+}
+
+func prefixedNames(fullName string) (prefixed string) {
+    parts := strings.Split(fullName, ",")
+    for i, name := range parts {
+        name = strings.Trim(name, " ")
+        prefixed += prefixFor(name) + name
+        if i < len(parts)-1 {
+            prefixed += ", "
+        }
+    }
+    return
+}
+
+func withEnvHint(envVar, str string) string {
+    envText := ""
+    if envVar != "" {
+        envText = fmt.Sprintf(" [$%s]", strings.Join(strings.Split(envVar, ","), ", $"))
+    }
+    return str + envText
+}
+
+func (self DirectoryFlag) getName() string {
+    return self.Name
+}
+
+func (self *DirectoryFlag) Set(value string) {
+    self.Value.Value = value
+}
+
+// Expands a file path
+// 1. replace tilde with users home dir
+// 2. expands embedded environment variables
+// 3. cleans the path, e.g. /a/b/../c -> /a/c
+// Note, it has limitations, e.g. ~someuser/tmp will not be expanded
+func expandPath(p string) string {
+    if strings.HasPrefix(p, "~/") || strings.HasPrefix(p, "~\\") {
+        if user, err := user.Current(); err == nil {
+            if err == nil {
+                p = strings.Replace(p, "~", user.HomeDir, 1)
+            }
+        }
+    }
+
+    return filepath.Clean(os.ExpandEnv(p))
+}
+
+
+
diff --git a/cmd/utils/customflags_test.go b/cmd/utils/customflags_test.go
new file mode 100644
index 000000000..5674b939e
--- /dev/null
+++ b/cmd/utils/customflags_test.go
@@ -0,0 +1,28 @@
+package utils
+
+import (
+    "testing"
+    "os"
+    "os/user"
+)
+
+func TestPathExpansion(t *testing.T) {
+
+    user, _ := user.Current()
+
+    tests := map[string]string {
+        "/home/someuser/tmp": "/home/someuser/tmp",
+        "~/tmp": user.HomeDir + "/tmp",
+        "$DDDXXX/a/b": "/tmp/a/b",
+        "/a/b/": "/a/b",
+    }
+
+    os.Setenv("DDDXXX", "/tmp")
+
+    for test, expected := range tests {
+        got := expandPath(test)
+        if got != expected {
+            t.Errorf("test %s, got %s, expected %s\n", test, got, expected)
+        }
+    }
+}
diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index 51844a68e..461d34ebc 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -68,10 +68,10 @@ func NewApp(version, usage string) *cli.App {
 
 var (
 	// General settings
-	DataDirFlag = cli.StringFlag{
-		Name:  "datadir",
+	DataDirFlag = DirectoryFlag{
+		Name: "datadir",
 		Usage: "Data directory to be used",
-		Value: common.DefaultDataDir(),
+		Value: DirectoryString{common.DefaultDataDir()},
 	}
 	ProtocolVersionFlag = cli.IntFlag{
 		Name:  "protocolversion",