feat: Add Go examples for process management

- Add Linux-specific cgo functions to set and get process titles.
- Add a demonstration of getting a child process's PID.
- Add an example of using 'exec -a' to set a child process title.

exec_with_title.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+// ExecWithTitle executes a command with a custom process title visible to `ps` on Linux.
+// It uses `bash -c "exec -a ..."` to achieve this.
+// title: The custom title for the process.
+// commandAndArgs: The command and its arguments to execute.
+func ExecWithTitle(title string, commandAndArgs ...string) error {
+	if len(commandAndArgs) == 0 {
+		return fmt.Errorf("no command provided to execute")
+	}
+
+	// The command to run is the first element.
+	command := commandAndArgs[0]
+	// The rest are its arguments.
+	args := commandAndArgs[1:]
+
+	// We need to construct the full command string for the shell.
+	// Using fmt.Sprintf with %q is a simple way to handle basic shell quoting.
+	// The final command will look like: exec -a 'My Title' 'sleep' '30'
+	fullCommand := fmt.Sprintf("exec -a %q %q %s",
+		title,
+		command,
+		strings.Join(quoteArgs(args), " "),
+	)
+
+	// The actual command we run is bash with the "-c" flag and our constructed string.
+	cmd := exec.Command("bash", "-c", fullCommand)
+
+	fmt.Printf("Running command: %s\n", cmd.String())
+
+	// Start the process.
+	err := cmd.Start()
+	if err != nil {
+		return fmt.Errorf("failed to start command: %w", err)
+	}
+
+	fmt.Printf("--> Process started with PID %d. Check 'ps aux | grep %d'.\n", cmd.Process.Pid, cmd.Process.Pid)
+	fmt.Println("--> The title should appear as:", title)
+	fmt.Println("Waiting for command to complete...")
+
+	// Wait for the command to complete.
+	return cmd.Wait()
+}
+
+// quoteArgs is a helper to wrap each argument in quotes for the shell.
+func quoteArgs(args []string) []string {
+	quoted := make([]string, len(args))
+	for i, arg := range args {
+		quoted[i] = fmt.Sprintf("%q", arg)
+	}
+	return quoted
+}
+
+func main() {
+	fmt.Println("Starting a 'sleep 30' process with a custom title...")
+	fmt.Println("You will have 30 seconds to run 'ps' in another terminal to see it.")
+
+	err := ExecWithTitle("My Custom Sleeper (Job #42)", "sleep", "30")
+	if err != nil {
+		fmt.Printf("\nCommand finished with error: %v\n", err)
+	} else {
+		fmt.Println("\nCommand finished successfully.")
+	}
+}

get_pid.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+	"os/exec"
+)
+
+func main() {
+	fmt.Println("Starting a 'sleep 15' command...")
+
+	// 1. Create the command.
+	cmd := exec.Command("sleep", "15")
+
+	// 2. Start the command. This is non-blocking.
+	err := cmd.Start()
+	if err != nil {
+		fmt.Printf("Error starting command: %v\n", err)
+		return
+	}
+
+	// 3. If Start() succeeded, the PID is now available.
+	// The check for err != nil above is critical to prevent a panic
+	// from a nil pointer dereference on cmd.Process.
+	pid := cmd.Process.Pid
+	fmt.Printf("--> Successfully started process with PID: %d\n", pid)
+	fmt.Println("--> You can verify this with 'ps aux | grep", pid, "'")
+
+	fmt.Println("Waiting for the process to finish in the background...")
+
+	// 4. Wait for the command to complete and release its resources.
+	err = cmd.Wait()
+	if err != nil {
+		fmt.Printf("Command finished with error: %v\n", err)
+	} else {
+		fmt.Println("Command finished successfully.")
+	}
+}

proctitle_demo.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/erikdubbelboer/gspt"
+)
+
+func main() {
+	// The initial process title is os.Args[0]
+	fmt.Printf("PID: %d\n", os.Getpid())
+	fmt.Println("Initial process title should be 'proctitle_demo'")
+	fmt.Println("Run 'ps -f -p ", os.Getpid(), "' in another terminal to check.")
+	time.Sleep(15 * time.Second)
+
+	// Set a new process title
+	newTitle := "proctitle_demo (processing data)"
+	gspt.SetProcTitle(newTitle)
+
+	fmt.Println("\nProcess title changed!")
+	fmt.Println("New title should be:", newTitle)
+	fmt.Println("Run 'ps -f -p ", os.Getpid(), "' again to see the change.")
+
+	// Keep the process alive to give you time to check
+	for {
+		time.Sleep(10 * time.Second)
+	}
+}
+

proctitle_linux.go

@@ -0,0 +1,138 @@
+//go:build linux
+
+package main
+
+/*
+#include <string.h>
+#include <stdlib.h>
+
+// Pointers to the original argv memory block.
+// These are populated by the init() constructor function before Go's main runs.
+static char **argv_start = NULL;
+static int argv_len = 0;
+
+// A C constructor function that runs before the Go runtime initializes.
+// It saves the original argc and argv passed to the program.
+__attribute__((constructor))
+static void init(int argc, char **argv) {
+	if (argc == 0 || argv == NULL || *argv == NULL) {
+		return;
+	}
+
+	// Calculate the total length of the memory occupied by the arguments.
+	// This is the maximum length our new title can be.
+	for (int i = 0; i < argc; i++) {
+		// The space for the argument string plus the null terminator.
+		argv_len += strlen(argv[i]) + 1;
+	}
+	// The last argument is followed by a NULL pointer, so we back up one byte
+	// from that to get to the final null terminator of the last argument string.
+	argv_len--;
+
+	argv_start = argv;
+}
+
+// set_title performs the actual memory modification.
+static void set_title(const char *title) {
+	// If argv_start is null, the constructor didn't run, so we can't do anything.
+	if (argv_start == NULL) {
+		return;
+	}
+
+	// Check if the new title is too long.
+	int title_len = strlen(title);
+	if (title_len >= argv_len) {
+		// If it is, we can't safely set it, so we do nothing.
+		return;
+	}
+
+	// Copy the new title into the argument memory.
+	strcpy(argv_start[0], title);
+
+	// Zero out the rest of the original argument memory space.
+	// This is important to prevent old argument data from appearing in `ps`.
+	memset(argv_start[0] + title_len, 0, argv_len - title_len);
+
+	// Some systems might need the pointer after the first argument to be NULL.
+	if (argv_start[1] != NULL) {
+		argv_start[1] = NULL;
+	}
+}
+*/
+import "C"
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"time"
+	"unsafe"
+)
+
+// SetProcTitle sets the process title for `ps` to display.
+// This is a Linux-only implementation using cgo.
+// The new title cannot be longer than the original command line string.
+func SetProcTitle(title string) {
+	// C.CString allocates memory in the C heap. We must free it.
+	cs := C.CString(title)
+	defer C.free(unsafe.Pointer(cs))
+	C.set_title(cs)
+}
+
+// GetProcTitle retrieves the current process title as seen by `ps`.
+// This is a Linux-only implementation that reads the special /proc/self/cmdline file.
+func GetProcTitle() (string, error) {
+	// On Linux, the kernel exposes the command line of a process in /proc/[pid]/cmdline.
+	// /proc/self is a symlink to the current process's directory.
+	// The arguments are separated by null bytes.
+	cmdlineBytes, err := os.ReadFile("/proc/self/cmdline")
+	if err != nil {
+		return "", fmt.Errorf("could not read /proc/self/cmdline: %w", err)
+	}
+
+	// The process title we set is the first null-terminated string in this file.
+	// We find the first null byte to isolate the title.
+	firstNull := bytes.IndexByte(cmdlineBytes, 0)
+	if firstNull == -1 {
+		// This would be unusual, but if there are no nulls, return the whole content.
+		return string(cmdlineBytes), nil
+	}
+
+	return string(cmdlineBytes[:firstNull]), nil
+}
+
+func main() {
+	pid := os.Getpid()
+	fmt.Printf("PID: %d\n", pid)
+
+	// Get and show the initial title
+	initialTitle, err := GetProcTitle()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Could not get initial title: %v\n", err)
+	} else {
+		fmt.Printf("Initial title via GetProcTitle(): '%s'\n", initialTitle)
+	}
+
+	fmt.Printf("--> Check it now with: ps -f -p %d\n", pid)
+	fmt.Println("Waiting 15 seconds before changing the title...")
+	time.Sleep(15 * time.Second)
+
+	// Now, set a new title.
+	newTitle := "MyGoProcess (processing tasks)"
+	fmt.Printf("\nSetting title to: '%s'\n", newTitle)
+	SetProcTitle(newTitle)
+
+	// Get and show the new title to confirm it was set
+	readTitle, err := GetProcTitle()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Could not get new title: %v\n", err)
+	} else {
+		fmt.Printf("Retrieved title via GetProcTitle(): '%s'\n", readTitle)
+	}
+
+	fmt.Printf("--> Check it again with: ps -f -p %d\n", pid)
+	fmt.Println("The process will exit in 15 seconds.")
+	time.Sleep(15 * time.Second)
+
+	fmt.Println("\nDone.")
+}