Add shared functions for quoting shell words

Author: cbandy

internal/patroni/config.go

@@ -15,6 +15,7 @@ import (
 	"github.com/crunchydata/postgres-operator/internal/config"
 	"github.com/crunchydata/postgres-operator/internal/naming"
 	"github.com/crunchydata/postgres-operator/internal/postgres"
+	"github.com/crunchydata/postgres-operator/internal/shell"
 	"github.com/crunchydata/postgres-operator/pkg/apis/postgres-operator.crunchydata.com/v1beta1"
 )
 
@@ -34,12 +35,6 @@ const (
 		"# Your changes will not be saved.\n"
 )
 
-// quoteShellWord ensures that s is interpreted by a shell as single word.
-func quoteShellWord(s string) string {
-	// https://www.gnu.org/software/bash/manual/html_node/Quoting.html
-	return `'` + strings.ReplaceAll(s, `'`, `'"'"'`) + `'`
-}
-
 // clusterYAML returns Patroni settings that apply to the entire cluster.
 func clusterYAML(
 	cluster *v1beta1.PostgresCluster,
@@ -581,15 +576,11 @@ func instanceYAML(
 			"-",
 		}, command...)
 
-		quoted := make([]string, len(command))
-		for i := range command {
-			quoted[i] = quoteShellWord(command[i])
-		}
 		postgresql[pgBackRestCreateReplicaMethod] = map[string]any{
-			"command":   strings.Join(quoted, " "),
-			"keep_data": true,
-			"no_leader": true,
-			"no_params": true,
+			"command":   strings.Join(shell.QuoteWords(command...), " "),
+			"keep_data": true, // Use the data directory from a prior method.
+			"no_leader": true, // Works without a replication connection.
+			"no_params": true, // Patroni should not add "--scope", "--role", etc.
 		}
 		methods = append([]string{pgBackRestCreateReplicaMethod}, methods...)
 	}

internal/shell/quote.go

@@ -0,0 +1,34 @@
+// Copyright 2024 - 2025 Crunchy Data Solutions, Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package shell
+
+import "strings"
+
+// escapeSingleQuoted is used by [QuoteWord].
+var escapeSingleQuoted = strings.NewReplacer(
+	// slightly shorter results for the unlikely pair of quotes.
+	`''`, `'"''"'`,
+
+	// first, close the single-quote U+0027,
+	// add one between double-quotes U+0022,
+	// then reopen the single-quote U+0027.
+	`'`, `'"'"'`,
+).Replace
+
+// QuoteWord ensures that v is interpreted by a shell as a single word.
+func QuoteWord(v string) string {
+	// https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html
+	// https://www.gnu.org/software/bash/manual/html_node/Quoting.html
+	return `'` + escapeSingleQuoted(v) + `'`
+}
+
+// QuoteWords ensures that s is interpreted by a shell as individual words.
+func QuoteWords(s ...string) []string {
+	quoted := make([]string, len(s))
+	for i := range s {
+		quoted[i] = QuoteWord(s[i])
+	}
+	return quoted
+}

internal/shell/quote_test.go

@@ -0,0 +1,34 @@
+// Copyright 2024 - 2025 Crunchy Data Solutions, Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package shell
+
+import (
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestQuoteWord(t *testing.T) {
+	assert.Equal(t, QuoteWord(""), `''`,
+		"expected empty and single-quoted")
+
+	assert.Equal(t, QuoteWord("abc"), `'abc'`,
+		"expected single-quoted")
+
+	assert.Equal(t, QuoteWord(`a" b"c`), `'a" b"c'`,
+		"expected easy double-quotes")
+
+	assert.Equal(t, QuoteWord(`a' b'c`),
+		`'a'`+`"'"`+`' b'`+`"'"`+`'c'`,
+		"expected close-quote-open twice")
+
+	assert.Equal(t, QuoteWord(`a''b`),
+		`'a'`+`"''"`+`'b'`,
+		"expected close-quotes-open once")
+
+	assert.Equal(t, QuoteWord(`x''''y`),
+		`'x'`+`"''"`+`''`+`"''"`+`'y'`,
+		"expected close-quotes-open twice")
+}