kzonecheck: allows '-' as substitution for '/dev/stdin'

relates #727

doc/man/kzonecheck.1in

@@ -41,6 +41,13 @@ DNS server.
 .sp
 Please, refer to the \fBsemantic\-checks\fP configuration option in
 \fBknot.conf(5)\fP for the full list of available semantic checks.
+.SS Parameters
+.INDENT 0.0
+.TP
+\fIfilename\fP
+Path to the zone file to be checked. For reading from \fBstdin\fP use \fB/dev/stdin\fP
+or just \fB\-\fP\&.
+.UNINDENT
 .SS Options
 .INDENT 0.0
 .TP

doc/man_kzonecheck.rst

@@ -18,6 +18,13 @@ DNS server.
 Please, refer to the ``semantic-checks`` configuration option in
 :manpage:`knot.conf(5)` for the full list of available semantic checks.
 
+Parameters
+..........
+
+*filename*
+  Path to the zone file to be checked. For reading from **stdin** use **/dev/stdin**
+  or just **-**.
+
 Options
 .......
 

src/utils/kzonecheck/main.c

-/*  Copyright (C) 2020 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+/*  Copyright (C) 2021 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
 
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -28,6 +28,9 @@
 
 #define PROGRAM_NAME "kzonecheck"
 
+#define STDIN_SUBST "-"
+#define STDIN_REPL "/dev/stdin"
+
 static void print_help(void)
 {
 	printf("Usage: %s [parameters] <filename>\n"
@@ -120,6 +123,9 @@ int main(int argc, char *argv[])
 	}
 
 	char *filename = argv[optind];
+	if (strncmp(filename, STDIN_SUBST, sizeof(STDIN_SUBST)) == 0) {
+		filename = STDIN_REPL;
+	}
 
 	char *zonename;
 	if (origin == NULL) {