cat: adds --separator option to cat command

When using `rclone cat` to print the contents of several files, the
user may want to inject some separator between the files, such as a
comma or a newline. This patch adds a `--separator` option to the `cat`
command to make that possible. The default value remains an empty
string, `""`, maintaining the prior behavior of `rclone cat`.

Closes #6968

cmd/bisync/bisync_test.go

@@ -824,8 +824,9 @@ func touchFiles(ctx context.Context, dateStr string, f fs.Fs, dir, glob string)
 			err = nil
 			buf := new(bytes.Buffer)
 			size := obj.Size()
+			separator := ""
 			if size > 0 {
-				err = operations.Cat(ctx, f, buf, 0, size)
+				err = operations.Cat(ctx, f, buf, 0, size, []byte(separator))
 			}
 			info := object.NewStaticObjectInfo(remote, date, size, true, nil, f)
 			if err == nil {

cmd/cat/cat.go

@@ -21,6 +21,7 @@ var (
 	offset    = int64(0)
 	count     = int64(-1)
 	discard   = false
+	separator = string("")
 )
 
 func init() {
@@ -31,6 +32,7 @@ func init() {
 	flags.Int64VarP(cmdFlags, &offset, "offset", "", offset, "Start printing at offset N (or from end if -ve)")
 	flags.Int64VarP(cmdFlags, &count, "count", "", count, "Only print N characters")
 	flags.BoolVarP(cmdFlags, &discard, "discard", "", discard, "Discard the output instead of printing")
+	flags.StringVarP(cmdFlags, &separator, "separator", "", separator, "Separator to use between objects when printing multiple files")
 }
 
 var commandDefinition = &cobra.Command{
@@ -56,6 +58,18 @@ Use the |--head| flag to print characters only at the start, |--tail| for
 the end and |--offset| and |--count| to print a section in the middle.
 Note that if offset is negative it will count from the end, so
 |--offset -1 --count 1| is equivalent to |--tail 1|.
+
+Use the |--separator| flag to print a separator value between files. Be sure to
+shell-escape special characters. For example, to print a newline between
+files, use:
+
+* bash:
+
+      rclone --include "*.txt" --separator $'\n' cat remote:path/to/dir
+
+* powershell:
+
+      rclone --include "*.txt" --separator "|n" cat remote:path/to/dir
 `, "|", "`"),
 	Annotations: map[string]string{
 		"versionIntroduced": "v1.33",
@@ -82,7 +96,7 @@ Note that if offset is negative it will count from the end, so
 			w = io.Discard
 		}
 		cmd.Run(false, false, command, func() error {
-			return operations.Cat(context.Background(), fsrc, w, offset, count)
+			return operations.Cat(context.Background(), fsrc, w, offset, count, []byte(separator))
 		})
 	},
 }

docs/content/commands/rclone_cat.md

@@ -32,6 +32,18 @@ the end and `--offset` and `--count` to print a section in the middle.
 Note that if offset is negative it will count from the end, so
 `--offset -1 --count 1` is equivalent to `--tail 1`.
 
+Use the `--separator` flag to print a separator value between files. Be sure to
+shell-escape special characters. For example, to print a newline between
+files, use:
+
+* bash:
+
+      rclone --include "*.txt" --separator $'\n' cat remote:path/to/dir
+
+* powershell:
+
+      rclone --include "*.txt" --separator "`n" cat remote:path/to/dir
+
 
 ```
 rclone cat remote:path [flags]
@@ -45,6 +57,7 @@ rclone cat remote:path [flags]
       --head int           Only print the first N characters
   -h, --help               help for cat
       --offset int         Start printing at offset N (or from end if -ve)
+      --separator string   Separator to use between objects when printing multiple files
       --tail int           Only print the last N characters
 ```
 

fs/operations/operations.go

@@ -1259,7 +1259,7 @@ type readCloser struct {
 //
 // if count < 0 then it will be ignored
 // if count >= 0 then only that many characters will be output
-func Cat(ctx context.Context, f fs.Fs, w io.Writer, offset, count int64) error {
+func Cat(ctx context.Context, f fs.Fs, w io.Writer, offset, count int64, sep []byte) error {
 	var mu sync.Mutex
 	ci := fs.GetConfig(ctx)
 	return ListFn(ctx, f, func(o fs.Object) {
@@ -1301,6 +1301,13 @@ func Cat(ctx context.Context, f fs.Fs, w io.Writer, offset, count int64) error {
 			err = fs.CountError(err)
 			fs.Errorf(o, "Failed to send to output: %v", err)
 		}
+		if len(sep) >= 0 {
+			_, err = w.Write(sep)
+			if err != nil {
+				err = fs.CountError(err)
+				fs.Errorf(o, "Failed to send separator to output: %v", err)
+			}
+		}
 	})
 }
 

fs/operations/operations_test.go

@@ -531,21 +531,23 @@ func TestCat(t *testing.T) {
 	for _, test := range []struct {
 		offset    int64
 		count     int64
+		separator string
 		a         string
 		b         string
 	}{
-		{0, -1, "ABCDEFGHIJ", "012345678"},
+		{0, -1, "", "ABCDEFGHIJ", "012345678"},
-		{0, 5, "ABCDE", "01234"},
+		{0, 5, "", "ABCDE", "01234"},
-		{-3, -1, "HIJ", "678"},
+		{-3, -1, "", "HIJ", "678"},
-		{1, 3, "BCD", "123"},
+		{1, 3, "", "BCD", "123"},
+		{0, -1, "\n", "ABCDEFGHIJ", "012345678"},
 	} {
 		var buf bytes.Buffer
-		err := operations.Cat(ctx, r.Fremote, &buf, test.offset, test.count)
+		err := operations.Cat(ctx, r.Fremote, &buf, test.offset, test.count, []byte(test.separator))
 		require.NoError(t, err)
 		res := buf.String()
 
-		if res != test.a+test.b && res != test.b+test.a {
+		if res != test.a+test.separator+test.b+test.separator && res != test.b+test.separator+test.a+test.separator {
-			t.Errorf("Incorrect output from Cat(%d,%d): %q", test.offset, test.count, res)
+			t.Errorf("Incorrect output from Cat(%d,%d,%s): %q", test.offset, test.count, test.separator, res)
 		}
 	}
 }