Allow to override fileName with different value

README.rst

@@ -323,7 +323,51 @@ Now you can encrypt a file using::
 
 And decrypt it using::
 
-     $ sops --decrypt test.enc.yaml
+    $ sops --decrypt test.enc.yaml
+
+
+Encrypting and decrypting from other programs
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When using ``sops`` in scripts or from other programs, there are often situations where you do not want to write
+encrypted or decrypted data to disk. The best way to avoid this is to pass data to SOPS via stdin, and to let
+SOPS write data to stdout. By default, the encrypt and decrypt operations write data to stdout already. To pass
+data via stdin, you need to pass ``/dev/stdin`` as the input filename. Please note that this only works on
+Unix-like operating systems such as macOS and Linux. On Windows, you have to use named pipes.
+
+To decrypt data, you can simply do:
+
+.. code:: sh
+
+	$ cat encrypted-data | sops --decrypt /dev/stdin > decrypted-data
+
+To control the input and output format, pass ``--input-type`` and ``--output-type`` as appropriate. By default,
+``sops`` determines the input and output format from the provided filename, which is ``/dev/stdin`` here, and
+thus will use the binary store which expects JSON input and outputs binary data on decryption.
+
+For example, to decrypt YAML data and obtain the decrypted result as YAML, use:
+
+.. code:: sh
+
+	$ cat encrypted-data | sops --input-type yaml --output-type yaml --decrypt /dev/stdin > decrypted-data
+
+To encrypt, it is important to note that SOPS also uses the filename to look up the correct creation rule from
+``.sops.yaml``. Likely ``/dev/stdin`` will not match a creation rule, or only match the fallback rule without
+``path_regex``, which is usually not what you want. For that, ``sops`` provides the ``--filename-override``
+parameter which allows you to tell SOPS which filename to use to match creation rules:
+
+.. code:: sh
+
+	$ echo 'foo: bar' | sops --filename-override path/filename.sops.yaml --encrypt /dev/stdin > encrypted-data
+
+SOPS will find a matching creation rule for ``path/filename.sops.yaml`` in ``.sops.yaml`` and use that one to
+encrypt the data from stdin. This filename will also be used to determine the input and output store. As always,
+the input store type can be adjusted by passing ``--input-type``, and the output store type by passing
+``--output-type``:
+
+.. code:: sh
+
+	$ echo foo=bar | sops --filename-override path/filename.sops.yaml --input-type dotenv --encrypt /dev/stdin > encrypted-data
 
 
 Encrypting using Hashicorp Vault

cmd/sops/main.go

@@ -769,6 +769,10 @@ func main() {
 			Name:  "output",
 			Usage: "Save the output after encryption or decryption to the file specified",
 		},
+		cli.StringFlag{
+			Name:  "filename-override",
+			Usage: "Use this filename instead of the provided argument for loading configuration, and for determining input type and output type",
+		},
 	}, keyserviceFlags...)
 
 	app.Action = func(c *cli.Context) error {
@@ -795,13 +799,17 @@ func main() {
 				return common.NewExitError("Error: cannot operate on non-existent file", codes.NoFileSpecified)
 			}
 		}
+		fileNameOverride := c.String("filename-override")
+		if fileNameOverride == "" {
+			fileNameOverride = fileName
+		}
 
 		unencryptedSuffix := c.String("unencrypted-suffix")
 		encryptedSuffix := c.String("encrypted-suffix")
 		encryptedRegex := c.String("encrypted-regex")
 		unencryptedRegex := c.String("unencrypted-regex")
 		macOnlyEncrypted := c.Bool("mac-only-encrypted")
-		conf, err := loadConfig(c, fileName, nil)
+		conf, err := loadConfig(c, fileNameOverride, nil)
 		if err != nil {
 			return toExitError(err)
 		}
@@ -847,19 +855,19 @@ func main() {
 			unencryptedSuffix = sops.DefaultUnencryptedSuffix
 		}
 
-		inputStore := inputStore(c, fileName)
-		outputStore := outputStore(c, fileName)
+		inputStore := inputStore(c, fileNameOverride)
+		outputStore := outputStore(c, fileNameOverride)
 		svcs := keyservices(c)
 
 		var output []byte
 		if c.Bool("encrypt") {
 			var groups []sops.KeyGroup
-			groups, err = keyGroups(c, fileName)
+			groups, err = keyGroups(c, fileNameOverride)
 			if err != nil {
 				return toExitError(err)
 			}
 			var threshold int
-			threshold, err = shamirThreshold(c, fileName)
+			threshold, err = shamirThreshold(c, fileNameOverride)
 			if err != nil {
 				return toExitError(err)
 			}
@@ -1015,12 +1023,12 @@ func main() {
 			} else {
 				// File doesn't exist, edit the example file instead
 				var groups []sops.KeyGroup
-				groups, err = keyGroups(c, fileName)
+				groups, err = keyGroups(c, fileNameOverride)
 				if err != nil {
 					return toExitError(err)
 				}
 				var threshold int
-				threshold, err = shamirThreshold(c, fileName)
+				threshold, err = shamirThreshold(c, fileNameOverride)
 				if err != nil {
 					return toExitError(err)
 				}