fs: Allow on the fly remotes with :backend: syntax - fixes #2449

This change allows remotes to be created on the fly without a config
file by using the remote type prefixed with a : as the remote name, Eg
:s3: to make an s3 remote.

This assumes the user is supplying the backend config via command line
flags or environment variables.

docs/content/docs.md

@@ -133,6 +133,48 @@ It is recommended to use `copy` when copying individual files, not `sync`.
 They have pretty much the same effect but `copy` will use a lot less
 memory.
 
+Syntax of remote paths
+----------------------
+
+The syntax of the paths passed to the rclone command are as follows.
+
+### /path/to/dir
+
+This refers to the local file system.
+
+On Windows only `\` may be used instead of `/` in local paths
+**only**, non local paths must use `/`.
+
+These paths needn't start with a leading `/` - if they don't then they
+will be relative to the current directory.
+
+### remote:path/to/dir
+
+This refers to a directory `path/to/dir` on `remote:` as defined in
+the config file (configured with `rclone config`).
+
+### remote:/path/to/dir
+
+On most backends this is refers to the same directory as
+`remote:path/to/dir` and that format should be preferred.  On a very
+small number of remotes (FTP, SFTP, Dropbox for business) this will
+refer to a different directory.  On these, paths without a leading `/`
+will refer to your "home" directory and paths with a leading `/` will
+refer to the root.
+
+### :backend:path/to/dir
+
+This is an advanced form for creating remotes on the fly.  `backend`
+should be the name or prefix of a backend (the `type` in the config
+file) and all the configuration for the backend should be provided on
+the command line (or in environment variables).
+
+Eg
+
+    rclone lsd --http-url https://pub.rclone.org :http:
+
+Which lists all the directories in `pub.rclone.org`.
+
 Quoting and the shell
 ---------------------
 

docs/content/http.md

@@ -121,17 +121,7 @@ No checksums are stored.
 
 ### Usage without a config file ###
 
-Note that since only two environment variable need to be set, it is
-easy to use without a config file like this.
+Since the http remote only has one config parameter it is easy to use
+without a config file:
 
-```
-RCLONE_CONFIG_ZZ_TYPE=http RCLONE_CONFIG_ZZ_URL=https://beta.rclone.org rclone lsd zz:
-```
-
-Or if you prefer
-
-```
-export RCLONE_CONFIG_ZZ_TYPE=http
-export RCLONE_CONFIG_ZZ_URL=https://beta.rclone.org
-rclone lsd zz:
-```
+    rclone lsd --http-url https://beta.rclone.org :http:

fs/fs.go

@@ -859,10 +859,14 @@ func ParseRemote(path string) (fsInfo *RegInfo, configName, fsPath string, err e
 	var fsName string
 	var ok bool
 	if configName != "" {
-		m := ConfigMap(nil, configName)
-		fsName, ok = m.Get("type")
-		if !ok {
-			return nil, "", "", ErrorNotFoundInConfigFile
+		if strings.HasPrefix(configName, ":") {
+			fsName = configName[1:]
+		} else {
+			m := ConfigMap(nil, configName)
+			fsName, ok = m.Get("type")
+			if !ok {
+				return nil, "", "", ErrorNotFoundInConfigFile
+			}
 		}
 	} else {
 		fsName = "local"

fs/fspath/path.go

@@ -10,7 +10,7 @@ import (
 )
 
 // Matcher is a pattern to match an rclone URL
-var Matcher = regexp.MustCompile(`^([\w_ -]+):(.*)$`)
+var Matcher = regexp.MustCompile(`^(:?[\w_ -]+):(.*)$`)
 
 // Parse deconstructs a remote path into configName and fsPath
 //

fs/fspath/path_test.go

@@ -16,6 +16,7 @@ func TestParse(t *testing.T) {
 		{"path/to/file", "", "path/to/file"},
 		{"remote:path/to/file", "remote", "path/to/file"},
 		{"remote:/path/to/file", "remote", "/path/to/file"},
+		{":backend:/path/to/file", ":backend", "/path/to/file"},
 	} {
 		gotConfigName, gotFsPath := Parse(test.in)
 		assert.Equal(t, test.wantConfigName, gotConfigName)
@@ -28,12 +29,21 @@ func TestSplit(t *testing.T) {
 		remote, wantParent, wantLeaf string
 	}{
 		{"", "", ""},
+
 		{"remote:", "remote:", ""},
 		{"remote:potato", "remote:", "potato"},
 		{"remote:/", "remote:/", ""},
 		{"remote:/potato", "remote:/", "potato"},
 		{"remote:/potato/potato", "remote:/potato/", "potato"},
 		{"remote:potato/sausage", "remote:potato/", "sausage"},
+
+		{":remote:", ":remote:", ""},
+		{":remote:potato", ":remote:", "potato"},
+		{":remote:/", ":remote:/", ""},
+		{":remote:/potato", ":remote:/", "potato"},
+		{":remote:/potato/potato", ":remote:/potato/", "potato"},
+		{":remote:potato/sausage", ":remote:potato/", "sausage"},
+
 		{"/", "/", ""},
 		{"/root", "/", "root"},
 		{"/a/b", "/a/", "b"},