Update documentation and add more escape options

README.md

@@ -19,7 +19,8 @@ Docker buildkit build with a key stored in Google Cloud KMS:
 export SSH_KEY_PATH=kms://projects/yourprojectname/locations/global/keyRings/yourkeyring/cryptoKeys/ssh-key/cryptoKeyVersions/1
 export PROGRESS_NO_TRUNC=1
 export DOCKER_BUILDKIT=1
-auth-wrapper docker --progress=plain --ssh=default='$SSH_AUTH_SOCK' .
+# The strings $SSH_AUTH_SOCK and $$SSH_AUTH_SOCK will be replaced with socket in the arguments
+auth-wrapper docker --progress=plain --ssh=default='\$SSH_AUTH_SOCK' . # Note the escape to make sure we don't use the shells SSH_AUTH_SOCK
 ```
 
 [Dockerfile](./testdata/Dockerfile)
@@ -40,7 +41,7 @@ steps:
   - name: 'gcr.io/$PROJECT_ID/auth-wrapper.master:latest'
     args: ['build', '--progress=plain', '--ssh=default=$$SSH_AUTH_SOCK', '-tag=gcr.io/$PROJECT_ID/$REPO_NAME.$BRANCH_NAME:$COMMIT_SHA', '.']
     env:
-      - "SSH_KEY_PATH=kms://projects/connectedcars-staging/locations/global/keyRings/cloudbuilder/cryptoKeys/ssh-key/cryptoKeyVersions/3"
+      - "SSH_KEY_PATH=kms://projects/$PROJECT_ID/locations/global/keyRings/cloudbuilder/cryptoKeys/ssh-key/cryptoKeyVersions/1"
       - "PROGRESS_NO_TRUNC=1"
       - "DOCKER_BUILDKIT=1"
 images: ['gcr.io/$PROJECT_ID/$REPO_NAME.$BRANCH_NAME']

cmd/main.go

@@ -65,7 +65,9 @@ func runWithSSHAgent(command string, args []string, sshKeyPath string, sshKeyPas
 
 		// Do string replacement for SSH_AUTH_SOCK
 		for i, arg := range args {
+			fmt.Fprintf(os.Stderr, "arg[%d]: %s\n", i, arg)
 			args[i] = strings.ReplaceAll(arg, "$SSH_AUTH_SOCK", sshAuthSock)
+			args[i] = strings.ReplaceAll(arg, "$$SSH_AUTH_SOCK", sshAuthSock)
 		}
 
 	}