Allow the binary to be symlinked to its toolnames 'ctfetch' and 'ctail'

.gitignore

@@ -1 +1,3 @@
 /ctool
+/ctfetch
+/ctail

cmd/ctool/cmd_fetch.go

@@ -18,12 +18,13 @@ func runFetch(args []string) {
 	logsListURL := fs.String("logs-list-url", "https://www.gstatic.com/ct/log_list/v3/all_logs_list.json", "URL of the CT log list JSON")
 	monitoringURL := fs.String("monitoring-url", "", "log root URL for issuer lookups when input is a file")
 	fs.Usage = func() {
+		n := cmdName("fetch")
 		fmt.Fprintf(os.Stderr, "Usage:\n")
-		fmt.Fprintf(os.Stderr, "  ctool fetch [flags] <log-url> <leaf-index> [+sct] [+issuer] [+ctlog] [+all]  fetch one entry\n")
+		fmt.Fprintf(os.Stderr, "  %s [flags] <log-url> <leaf-index> [+sct] [+issuer] [+ctlog] [+all]  fetch one entry\n", n)
-		fmt.Fprintf(os.Stderr, "  ctool fetch [flags] <tile-url-or-file> [+sct] [+issuer] [+ctlog] [+all]      dump all entries in a tile\n")
+		fmt.Fprintf(os.Stderr, "  %s [flags] <tile-url-or-file> [+sct] [+issuer] [+ctlog] [+all]      dump all entries in a tile\n", n)
 		fmt.Fprintf(os.Stderr, "\nExamples:\n")
-		fmt.Fprintf(os.Stderr, "  ctool fetch https://halloumi2026h1.mon.ct.ipng.ch 629794635 +all\n")
+		fmt.Fprintf(os.Stderr, "  %s https://halloumi2026h1.mon.ct.ipng.ch 629794635 +all\n", n)
-		fmt.Fprintf(os.Stderr, "  ctool fetch https://halloumi2026h1.mon.ct.ipng.ch/tile/data/x002/x460/135 +sct\n")
+		fmt.Fprintf(os.Stderr, "  %s https://halloumi2026h1.mon.ct.ipng.ch/tile/data/x002/x460/135 +sct\n", n)
 		fmt.Fprintf(os.Stderr, "\nFlags:\n")
 		fs.PrintDefaults()
 	}

cmd/ctool/cmd_tail.go

@@ -31,11 +31,12 @@ func runTail(args []string) {
 	rateLimitFlag := fs.Duration("rate-limit", 2*time.Second, "minimum time between HTTP requests (minimum 100ms)")
 	fs.StringVar(&userAgent, "user-agent", "ctool/"+version+" (https://git.ipng.ch/certificate-transparency/)", "User-Agent header for HTTP requests")
 	fs.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage: ctool tail [flags] <log-url>\n")
+		n := cmdName("tail")
+		fmt.Fprintf(os.Stderr, "Usage: %s [flags] <log-url>\n", n)
 		fmt.Fprintf(os.Stderr, "\nPrints a one-liner per cert/pre-cert as new entries arrive in a Static CT log.\n")
 		fmt.Fprintf(os.Stderr, "\nExamples:\n")
-		fmt.Fprintf(os.Stderr, "  ctool tail https://halloumi2026h2.mon.ct.ipng.ch\n")
+		fmt.Fprintf(os.Stderr, "  %s https://halloumi2026h2.mon.ct.ipng.ch\n", n)
-		fmt.Fprintf(os.Stderr, "  ctool tail --from-leaf 0 --interval 10s https://halloumi2026h2.mon.ct.ipng.ch\n")
+		fmt.Fprintf(os.Stderr, "  %s --from-leaf 0 --interval 10s https://halloumi2026h2.mon.ct.ipng.ch\n", n)
 		fmt.Fprintf(os.Stderr, "\nFlags:\n")
 		fs.PrintDefaults()
 	}

cmd/ctool/main.go

@@ -8,11 +8,23 @@ package main
 import (
 	"fmt"
 	"os"
+	"path/filepath"
+	"strings"
 )
 
 const version = "0.1.0"
 
 func main() {
+	// Busybox-style: if invoked as "ctfetch" or "ctail", shortcut to that command.
+	switch strings.TrimSuffix(filepath.Base(os.Args[0]), filepath.Ext(os.Args[0])) {
+	case "ctfetch":
+		runFetch(os.Args[1:])
+		return
+	case "ctail":
+		runTail(os.Args[1:])
+		return
+	}
+
 	if len(os.Args) < 2 {
 		usage()
 		os.Exit(1)
@@ -42,3 +54,14 @@ func fatal(format string, args ...any) {
 	fmt.Fprintf(os.Stderr, "Error: "+format+"\n", args...)
 	os.Exit(1)
 }
+
+// cmdName returns the effective command name for usage messages.
+// When invoked via a symlink (e.g. "ctfetch"), it returns that name directly.
+// Otherwise it returns "ctool <sub>" (e.g. "ctool fetch").
+func cmdName(sub string) string {
+	base := strings.TrimSuffix(filepath.Base(os.Args[0]), filepath.Ext(os.Args[0]))
+	if base == "ctool" {
+		return "ctool " + sub
+	}
+	return base
+}