hashsum: support creating hash from data received on stdin

See #5781

cmd/sha1sum/sha1sum.go

@@ -13,7 +13,7 @@ import (
 func init() {
 	cmd.Root.AddCommand(commandDefinition)
 	cmdFlags := commandDefinition.Flags()
-	hashsum.AddHashFlags(cmdFlags)
+	hashsum.AddHashsumFlags(cmdFlags)
 }
 
 var commandDefinition = &cobra.Command{
@@ -27,9 +27,20 @@ By default, the hash is requested from the remote.  If SHA-1 is
 not supported by the remote, no hash will be returned.  With the
 download flag, the file will be downloaded from the remote and
 hashed locally enabling SHA-1 for any remote.
+
+This command can also hash data received on standard input (stdin),
+by not passing a remote:path, or by passing a hyphen as remote:path
+when there is data to read (if not, the hypen will be treated literaly,
+as a relative path).
+
+This command can also hash data received on STDIN, if not passing
+a remote:path.
 `,
-	Run: func(command *cobra.Command, args []string) {
-		cmd.CheckArgs(1, 1, command, args)
+	RunE: func(command *cobra.Command, args []string) error {
+		cmd.CheckArgs(0, 1, command, args)
+		if found, err := hashsum.CreateFromStdinArg(hash.SHA1, args, 0); found {
+			return err
+		}
 		fsrc := cmd.NewFsSrc(args)
 		cmd.Run(false, false, command, func() error {
 			if hashsum.ChecksumFile != "" {
@@ -46,5 +57,6 @@ hashed locally enabling SHA-1 for any remote.
 			defer close()
 			return operations.HashLister(context.Background(), hash.SHA1, hashsum.OutputBase64, hashsum.DownloadFlag, fsrc, output)
 		})
+		return nil
 	},
 }