convmv: add convmv command

convmv supports advanced path name transformations for converting and renaming
files and directories by applying prefixes, suffixes, and other alterations.

For example:

rclone convmv "stories/The Quick Brown Fox!.txt" --name-transform "all,uppercase"
// Output: STORIES/THE QUICK BROWN FOX!.TXT

See help doc for complete details.

cmd/convmv/convmv.go

@@ -0,0 +1,108 @@
+// Package convmv provides the convmv command.
+package convmv
+
+import (
+	"context"
+	"errors"
+	"strings"
+
+	"github.com/rclone/rclone/cmd"
+	"github.com/rclone/rclone/fs/config/flags"
+	"github.com/rclone/rclone/fs/operations"
+	"github.com/rclone/rclone/fs/sync"
+	"github.com/rclone/rclone/lib/transform"
+	"github.com/spf13/cobra"
+)
+
+// Globals
+var (
+	deleteEmptySrcDirs = false
+	createEmptySrcDirs = false
+)
+
+func init() {
+	cmd.Root.AddCommand(commandDefinition)
+	cmdFlags := commandDefinition.Flags()
+	flags.BoolVarP(cmdFlags, &deleteEmptySrcDirs, "delete-empty-src-dirs", "", deleteEmptySrcDirs, "Delete empty source dirs after move", "")
+	flags.BoolVarP(cmdFlags, &createEmptySrcDirs, "create-empty-src-dirs", "", createEmptySrcDirs, "Create empty source dirs on destination after move", "")
+}
+
+var commandDefinition = &cobra.Command{
+	Use:   "convmv dest:path --name-transform XXX",
+	Short: `Convert file and directory names in place.`,
+	// Warning¡ "¡" will be replaced by backticks below
+	Long: strings.ReplaceAll(`
+convmv supports advanced path name transformations for converting and renaming files and directories by applying prefixes, suffixes, and other alterations.
+
+`+transform.SprintList()+`
+
+Multiple transformations can be used in sequence, applied in the order they are specified on the command line.
+
+The ¡--name-transform¡ flag is also available in ¡sync¡, ¡copy¡, and ¡move¡.
+
+## Files vs Directories ##
+
+By default ¡--name-transform¡ will only apply to file names. The means only the leaf file name will be transformed.
+However some of the transforms would be better applied to the whole path or just directories.
+To choose which which part of the file path is affected some tags can be added to the ¡--name-transform¡
+
+| Tag | Effect |
+|------|------|
+| ¡file¡ | Only transform the leaf name of files (DEFAULT) |
+| ¡dir¡ | Only transform name of directories - these may appear anywhere in the path |
+| ¡all¡ | Transform the entire path for files and directories |
+
+This is used by adding the tag into the transform name like this: ¡--name-transform file,prefix=ABC¡ or ¡--name-transform dir,prefix=DEF¡.
+
+For some conversions using all is more likely to be useful, for example ¡--name-transform all,nfc¡
+
+Note that ¡--name-transform¡ may not add path separators ¡/¡ to the name. This will cause an error.
+
+## Ordering and Conflicts ##
+
+* Transformations will be applied in the order specified by the user.
+    * If the ¡file¡ tag is in use (the default) then only the leaf name of files will be transformed.
+    * If the ¡dir¡ tag is in use then directories anywhere in the path will be transformed
+    * If the ¡all¡ tag is in use then directories and files anywhere in the path will be transformed
+    * Each transformation will be run one path segment at a time.
+    * If a transformation adds a ¡/¡ or ends up with an empty path segment then that will be an error.
+* It is up to the user to put the transformations in a sensible order.
+    * Conflicting transformations, such as ¡prefix¡ followed by ¡trimprefix¡ or ¡nfc¡ followed by ¡nfd¡, are possible.
+    * Instead of enforcing mutual exclusivity, transformations are applied in sequence as specified by the
+user, allowing for intentional use cases (e.g., trimming one prefix before adding another).
+    * Users should be aware that certain combinations may lead to unexpected results and should verify
+transformations using ¡--dry-run¡ before execution.
+
+## Race Conditions and Non-Deterministic Behavior ##
+
+Some transformations, such as ¡replace=old:new¡, may introduce conflicts where multiple source files map to the same destination name.
+This can lead to race conditions when performing concurrent transfers. It is up to the user to anticipate these.
+* If two files from the source are transformed into the same name at the destination, the final state may be non-deterministic.
+* Running rclone check after a sync using such transformations may erroneously report missing or differing files due to overwritten results.
+
+* To minimize risks, users should:
+    * Carefully review transformations that may introduce conflicts.
+    * Use ¡--dry-run¡ to inspect changes before executing a sync (but keep in mind that it won't show the effect of non-deterministic transformations).
+    * Avoid transformations that cause multiple distinct source files to map to the same destination name.
+    * Consider disabling concurrency with ¡--transfers=1¡ if necessary.
+    * Certain transformations (e.g. ¡prefix¡) will have a multiplying effect every time they are used. Avoid these when using ¡bisync¡.
+
+	`, "¡", "`"),
+	Annotations: map[string]string{
+		"versionIntroduced": "v1.70",
+		"groups":            "Filter,Listing,Important,Copy",
+	},
+	Run: func(command *cobra.Command, args []string) {
+		cmd.CheckArgs(1, 1, command, args)
+		fdst, srcFileName := cmd.NewFsFile(args[0])
+		cmd.Run(false, true, command, func() error {
+			if !transform.Transforming(context.Background()) {
+				return errors.New("--name-transform must be set")
+			}
+			if srcFileName == "" {
+				return sync.Transform(context.Background(), fdst, deleteEmptySrcDirs, createEmptySrcDirs)
+			}
+			return operations.TransformFile(context.Background(), fdst, srcFileName)
+		})
+	},
+}