From c9cca37ca6f7f62804bf53d2df2d5107523a572e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=A1=D0=B0=D1=85=D0=BD=D0=BE=D0=B2=20=D0=93=D0=BB=D0=B5?=
 =?UTF-8?q?=D0=B1=20=D0=90=D0=BD=D0=B4=D1=80=D0=B5=D0=B5=D0=B2=D0=B8=D1=87?=
 <Sakhnov.G.An@sberbank.ru>
Date: Sat, 4 Dec 2021 00:16:55 +0300
Subject: [PATCH] more verbose usage help

---
 cero.go | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/cero.go b/cero.go
index e7ccc4a..9811178 100644
--- a/cero.go
+++ b/cero.go
@@ -28,6 +28,11 @@ var (
 	onlyValidDomainNames bool
 )
 
+var usage = "" +
+	`usage: cero [options] [targets]
+if [targets] not provided in commandline arguments, will read from stdin
+`
+
 func main() {
 	// parse CLI arguments
 	var ports string
@@ -37,6 +42,14 @@ func main() {
 	flag.StringVar(&ports, "p", "443", "TLS ports to use, if not specified explicitly in host address. Use comma-separated list")
 	flag.IntVar(&timeout, "t", 4, "TLS Connection timeout in seconds")
 	flag.BoolVar(&onlyValidDomainNames, "d", false, "Output only valid domain names (e.g. strip IPs, wildcard domains and gibberish)")
+
+	// set custom usage text
+	flag.Usage = func() {
+		fmt.Fprintln(os.Stderr, usage)
+		fmt.Fprintln(os.Stderr, "options:")
+		flag.PrintDefaults()
+	}
+
 	flag.Parse()
 
 	// parse default port list into string slice