test: add examples for system package

docs/system.md

@@ -102,7 +102,7 @@ import (
 )
 
 func main() {
-	isOsMac := system.IsMac
+	isOsMac := system.IsMac()
 	fmt.Println(isOsMac)
 }
 ```

docs/system_zh-CN.md

@@ -26,7 +26,6 @@ import (
 - [GetOsEnv](#GetOsEnv)
 - [SetOsEnv](#SetOsEnv)
 - [RemoveOsEnv](#RemoveOsEnv)
-
 - [CompareOsEnv](#CompareOsEnv)
 - [ExecCommand](#ExecCommand)
 - [GetOsBits](#GetOsBits)
@@ -103,7 +102,7 @@ import (
 )
 
 func main() {
-	isOsMac := system.IsMac
+	isOsMac := system.IsMac()
 	fmt.Println(isOsMac)
 }
 ```

system/os.go

@@ -15,37 +15,44 @@ import (
 	"golang.org/x/text/encoding/simplifiedchinese"
 )
 
-// IsWindows check if current os is windows
+// IsWindows check if current os is windows.
+// Play: https://go.dev/play/p/XzJULbzmf9m
 func IsWindows() bool {
 	return runtime.GOOS == "windows"
 }
 
-// IsLinux check if current os is linux
+// IsLinux check if current os is linux.
+// Play: https://go.dev/play/p/zIflQgZNuxD
 func IsLinux() bool {
 	return runtime.GOOS == "linux"
 }
 
-// IsMac check if current os is macos
+// IsMac check if current os is macos.
+// Play: https://go.dev/play/p/Mg4Hjtyq7Zc
 func IsMac() bool {
 	return runtime.GOOS == "darwin"
 }
 
 // GetOsEnv gets the value of the environment variable named by the key.
+// Play: https://go.dev/play/p/D88OYVCyjO-
 func GetOsEnv(key string) string {
 	return os.Getenv(key)
 }
 
 // SetOsEnv sets the value of the environment variable named by the key.
+// Play: https://go.dev/play/p/D88OYVCyjO-
 func SetOsEnv(key, value string) error {
 	return os.Setenv(key, value)
 }
 
 // RemoveOsEnv remove a single environment variable.
+// Play: https://go.dev/play/p/fqyq4b3xUFQ
 func RemoveOsEnv(key string) error {
 	return os.Unsetenv(key)
 }
 
-// CompareOsEnv gets env named by the key and compare it with comparedEnv
+// CompareOsEnv gets env named by the key and compare it with comparedEnv.
+// Play: https://go.dev/play/p/BciHrKYOHbp
 func CompareOsEnv(key, comparedEnv string) bool {
 	env := GetOsEnv(key)
 	if env == "" {
@@ -58,6 +65,7 @@ func CompareOsEnv(key, comparedEnv string) bool {
 // param `command` is a complete command string, like, ls -a (linux), dir(windows), ping 127.0.0.1
 // in linux,  use /bin/bash -c to execute command
 // in windows, use powershell.exe to execute command
+// Play: https://go.dev/play/p/n-2fLyZef-4
 func ExecCommand(command string) (stdout, stderr string, err error) {
 	var out bytes.Buffer
 	var errOut bytes.Buffer
@@ -109,8 +117,8 @@ func byteToString(data []byte, charset string) string {
 	return result
 }
 
-// GetOsBits get this system bits 32bit or 64bit
-// return bit int (32/64)
+// GetOsBits return this system bits (32 or 64)
+// Play: https://go.dev/play/p/ml-_XH3gJbW
 func GetOsBits() int {
 	return 32 << (^uint(0) >> 63)
 }