Address Copilot review comments on perftrace command

- Fix regex pattern for consistency with other commands
- Fix README path to use forward slashes for cross-platform
- Add test cases for :PERFTRACE command parsing
- Add :perftrace assertion in TestHelpCommand
- Add TestPerftraceCommand for comprehensive testing

Author: dlevy-msft-sql

README.md

@@ -167,7 +167,7 @@ program_name          sqlcmd
 - `:perftrace` redirects performance statistics output to a file, stderr, or stdout. Use in conjunction with `-p` flag.
 
 ```
-1> :perftrace c:\logs\perf.txt
+1> :perftrace c:/logs/perf.txt
 1> select 1
 2> go
 ```

pkg/sqlcmd/commands.go

@@ -119,7 +119,7 @@ func newCommands() Commands {
 			name:   "HELP",
 		},
 		"PERFTRACE": {
-			regex:  regexp.MustCompile(`(?im)^[\t ]*?:PERFTRACE(?:[ \t]+(.*$)|$)`),
+			regex:  regexp.MustCompile(`(?im)^[ \t]*:PERFTRACE(?:[ \t]+(.*$)|$)`),
 			action: perftraceCommand,
 			name:   "PERFTRACE",
 		},

pkg/sqlcmd/commands_test.go

@@ -56,6 +56,8 @@ func TestCommandParsing(t *testing.T) {
 		{`RESET`, "RESET", []string{""}},
 		{`:HELP`, "HELP", []string{""}},
 		{`:help`, "HELP", []string{""}},
+		{`:PERFTRACE stderr`, "PERFTRACE", []string{"stderr"}},
+		{`:perftrace c:/logs/perf.txt`, "PERFTRACE", []string{"c:/logs/perf.txt"}},
 	}
 
 	for _, test := range commands {
@@ -478,6 +480,44 @@ func TestHelpCommand(t *testing.T) {
 	assert.Contains(t, output, ":listvar", "help should list :listvar")
 	assert.Contains(t, output, ":out", "help should list :out")
 	assert.Contains(t, output, ":error", "help should list :error")
+	assert.Contains(t, output, ":perftrace", "help should list :perftrace")
 	assert.Contains(t, output, ":r", "help should list :r")
 	assert.Contains(t, output, "go", "help should list go")
 }
+
+func TestPerftraceCommand(t *testing.T) {
+	s, buf := setupSqlCmdWithMemoryOutput(t)
+	defer buf.Close()
+
+	// Test empty argument returns error
+	err := perftraceCommand(s, []string{""}, 1)
+	assert.EqualError(t, err, InvalidCommandError("PERFTRACE", 1).Error(), "perftraceCommand with empty argument")
+
+	// Test redirect to stdout
+	err = perftraceCommand(s, []string{"stdout"}, 1)
+	assert.NoError(t, err, "perftraceCommand with stdout")
+	assert.Equal(t, os.Stdout, s.GetStat(), "stat set to stdout")
+
+	// Test redirect to stderr
+	err = perftraceCommand(s, []string{"stderr"}, 1)
+	assert.NoError(t, err, "perftraceCommand with stderr")
+	assert.Equal(t, os.Stderr, s.GetStat(), "stat set to stderr")
+
+	// Test redirect to file
+	file, err := os.CreateTemp("", "sqlcmdperf")
+	assert.NoError(t, err, "os.CreateTemp")
+	defer os.Remove(file.Name())
+	fileName := file.Name()
+	_ = file.Close()
+
+	err = perftraceCommand(s, []string{fileName}, 1)
+	assert.NoError(t, err, "perftraceCommand with file path")
+	// Clean up by setting stat to nil
+	s.SetStat(nil)
+
+	// Test variable resolution
+	s.vars.Set("myvar", "stdout")
+	err = perftraceCommand(s, []string{"$(myvar)"}, 1)
+	assert.NoError(t, err, "perftraceCommand with a variable")
+	assert.Equal(t, os.Stdout, s.GetStat(), "stat set to stdout using a variable")
+}