feat: add shell scripting with variables

Implemented roadmap #9: Shell scripts execution with variables.

Features:
- set <name> <value> - Set shell variable
- unset <name> - Remove variable
- vars - List all variables
- Variable substitution in all commands

Variable syntax:
- $VAR or ${VAR} - Shell variables
- $ENV:VARNAME - Environment variables

Variables expand before command execution, enabling:
- Dynamic key paths: put $BASE/$ID '{"data":"value"}'
- Reusable values: set TOKEN xyz && auth $TOKEN
- Script parameterization in batch files

Example batch script:
  set USER alice
  set KEY_PREFIX users
  put $KEY_PREFIX/$USER '{"name":"$USER"}'
  get $KEY_PREFIX/$USER

Variables are session-scoped and work in both interactive
and batch modes. Environment variables can be injected using
$ENV:HOME syntax.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

client.go

@@ -16,6 +16,7 @@ type KVSClient struct {
 	httpClient    *http.Client
 	profiles      map[string]Profile
 	activeProfile string
+	variables     map[string]string // Shell variables for scripting
 }
 
 // NewKVSClient creates a new KVS client instance
@@ -25,7 +26,8 @@ func NewKVSClient(baseURL string) *KVSClient {
 		httpClient: &http.Client{
 			Timeout: 30 * time.Second,
 		},
-		profiles: make(map[string]Profile),
+		profiles:  make(map[string]Profile),
+		variables: make(map[string]string),
 	}
 }
 

cmd_system.go

@@ -67,6 +67,13 @@ Export/Import:
     --skip-existing          - Skip existing keys (default)
     --overwrite              - Overwrite existing keys
 
+Shell Scripting:
+  set <name> <value>         - Set shell variable
+  unset <name>               - Remove shell variable
+  vars                       - List all variables
+    Variables: $VAR or ${VAR}
+    Environment: $ENV:VARNAME
+
 Batch Operations:
   batch <file>               - Execute commands from file
   source <file>              - Alias for batch

cmd_variables.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+	"strings"
+)
+
+// handleSet sets a shell variable
+func (c *KVSClient) handleSet(args []string) {
+	if len(args) < 2 {
+		fmt.Println(red("Usage: set <name> <value>"))
+		fmt.Println("Example: set USER_ID abc-123")
+		return
+	}
+
+	name := args[0]
+	value := strings.Join(args[1:], " ")
+
+	c.variables[name] = value
+	fmt.Printf(green("Set:")+" %s = %s\n", name, value)
+}
+
+// handleUnset removes a shell variable
+func (c *KVSClient) handleUnset(args []string) {
+	if len(args) < 1 {
+		fmt.Println(red("Usage: unset <name>"))
+		return
+	}
+
+	name := args[0]
+	if _, exists := c.variables[name]; exists {
+		delete(c.variables, name)
+		fmt.Println(green("Unset:"), name)
+	} else {
+		fmt.Println(yellow("Variable not set:"), name)
+	}
+}
+
+// handleVars lists all shell variables
+func (c *KVSClient) handleVars(args []string) {
+	if len(c.variables) == 0 {
+		fmt.Println(yellow("No variables set"))
+		return
+	}
+
+	fmt.Println(cyan("Shell Variables:"))
+	for name, value := range c.variables {
+		fmt.Printf("  %s = %s\n", name, value)
+	}
+}
+
+// expandVariables performs variable substitution on a string
+// Supports:
+// - $VAR or ${VAR} for shell variables
+// - $ENV:VAR for environment variables
+func (c *KVSClient) expandVariables(input string) string {
+	// Pattern for $VAR or ${VAR}
+	varPattern := regexp.MustCompile(`\$\{?([A-Za-z_][A-Za-z0-9_]*)\}?`)
+
+	// Pattern for $ENV:VAR
+	envPattern := regexp.MustCompile(`\$ENV:([A-Za-z_][A-Za-z0-9_]*)`)
+
+	// First, replace environment variables
+	result := envPattern.ReplaceAllStringFunc(input, func(match string) string {
+		varName := envPattern.FindStringSubmatch(match)[1]
+		if value, exists := os.LookupEnv(varName); exists {
+			return value
+		}
+		return match // Leave unchanged if not found
+	})
+
+	// Then, replace shell variables
+	result = varPattern.ReplaceAllStringFunc(result, func(match string) string {
+		varName := varPattern.FindStringSubmatch(match)[1]
+		if value, exists := c.variables[varName]; exists {
+			return value
+		}
+		return match // Leave unchanged if not found
+	})
+
+	return result
+}

main.go

@@ -10,6 +10,9 @@ import (
 
 // executeCommand executes a single command line
 func (c *KVSClient) executeCommand(line string) bool {
+	// Expand variables in the line
+	line = c.expandVariables(line)
+
 	parts := parseCommand(line)
 	if len(parts) == 0 {
 		return true
@@ -66,6 +69,12 @@ func (c *KVSClient) executeCommand(line string) bool {
 		c.handleImport(args)
 	case "export-list":
 		c.handleExportList(args)
+	case "set":
+		c.handleSet(args)
+	case "unset":
+		c.handleUnset(args)
+	case "vars":
+		c.handleVars(args)
 	case "batch", "source":
 		c.handleBatch(args, c.executeCommand)
 	default:

utils.go

@@ -130,6 +130,9 @@ var completer = readline.NewPrefixCompleter(
 	readline.PcItem("export"),
 	readline.PcItem("import"),
 	readline.PcItem("export-list"),
+	readline.PcItem("set"),
+	readline.PcItem("unset"),
+	readline.PcItem("vars"),
 	readline.PcItem("batch"),
 	readline.PcItem("source"),
 	readline.PcItem("help"),