listamsb: add -c (check only) option.

3 files changed, 44 insertions, 5 deletions

diff --git a/listamsb.1 b/listamsb.1
index 96e7dcb..37ece05 100644
--- a/listamsb.1
+++ b/listamsb.1
@@ -59,6 +59,10 @@ Output raw ATASCII. This option must be used with a pipe or redirection, as
 \fBlistamsb\fP will not write ATASCII to a terminal. \fBa8cat\fP is not used,
 with this option.
 .TP
+.B \fB\-c\fP
+Check only. No output on stdout. Diagnostics are still printed on stderr,
+and the exit status is unchanged.
+.TP
 .B \fB\-v\fP
 Verbose output, on stderr.
 .TP
@@ -67,8 +71,16 @@ Print built\-in help and exit.
 .TP
 .B \fB\-i\fP, \fB\-u\fP, \fB\-t\fP, \fB\-m\fP, \fB\-s\fP
 These options are passed to \fBa8cat\fP\&. See its man page for details. If
-the \fB\-a\fP option is used, these options have no effect.
+the \fB\-a\fP or \fB\-c\fP option is used, these options have no effect.
 .UNINDENT
+.SH DIAGNOSTICS
+.SH LIMITATIONS
+.sp
+Unlike \fBlistbas\fP, there\(aqs no color syntax highlighting. Probably there
+never will be.
+.sp
+It\(aqs hard to reliably detect AMSB files. If you feed \fBlistamsb\fP an
+Atari BASIC file, you\(aqll get gibberish output.
 .SH EXIT STATUS
 .sp
 0 for success, 1 if there was an error reading the input (e.g. file
diff --git a/listamsb.c b/listamsb.c
index efa0621..5d9b425 100644
--- a/listamsb.c
+++ b/listamsb.c
@@ -34,8 +34,9 @@ const char *self;
 
 char pipe_command[BUFSIZ + 1] = { "a8cat" };
 
-int verbose = 0;
-int raw_output = 0;
+int verbose = 0;     /* -v */
+int raw_output = 0;  /* -a */
+int check_only = 0;  /* -c */
 
 int need_pclose = 0;
 int bytes_read = 0;
@@ -208,6 +209,7 @@ void print_help(void) {
 	puts("By B. Watson <urchlay@slackware.uk>, released under the WTFPL");
 	printf("Usage: %s [-a] [-v] [-h] [-i] [-u] [-t] [-m] [-s] [file]\n", self);
 	puts("  -a: raw ATASCII output");
+	puts("  -c: check only (no listing)");
 	puts("  -v: verbose");
 	puts("  -h: show this help");
 	puts("  -i -u -t -m -s: passed to a8cat (try 'a8cat -h')");
@@ -218,8 +220,9 @@ void parse_args(int argc, char **argv) {
 	char tmp[10];
 	int opt;
 
-	while( (opt = getopt(argc, argv, "vaiutmsh")) != -1) {
+	while( (opt = getopt(argc, argv, "cvaiutmsh")) != -1) {
 		switch(opt) {
+			case 'c': check_only = 1; break;
 			case 'a': raw_output = 1; break;
 			case 'h': print_help(); exit(0);
 			case 'v': verbose = 1; break;
@@ -257,6 +260,14 @@ void parse_args(int argc, char **argv) {
 }
 
 void open_output() {
+	if(check_only) {
+		outfile = freopen("/dev/null", "wb", stdout);
+		if(!outfile) {
+			fprintf(stderr, "%s: ", self);
+			perror("/dev/null");
+			exit(1);
+		}
+	}
 	if(raw_output) {
 		if(isatty(fileno(stdout)))
 			die("refusing to write raw ATASCII to a terminal");
diff --git a/listamsb.rst b/listamsb.rst
index e6e2225..af72e73 100644
--- a/listamsb.rst
+++ b/listamsb.rst
@@ -41,6 +41,10 @@ OPTIONS
   **listamsb** will not write ATASCII to a terminal. **a8cat** is not used,
   with this option.
 
+**-c**
+  Check only. No output on stdout. Diagnostics are still printed on stderr,
+  and the exit status is unchanged.
+
 **-v**
   Verbose output, on stderr.
 
@@ -49,7 +53,19 @@ OPTIONS
 
 **-i**\, **-u**\, **-t**\, **-m**\, **-s**
   These options are passed to **a8cat**. See its man page for details. If
-  the **-a** option is used, these options have no effect.
+  the **-a** or **-c** option is used, these options have no effect.
+
+DIAGNOSTICS
+===========
+
+LIMITATIONS
+===========
+
+Unlike **listbas**, there's no color syntax highlighting. Probably there
+never will be.
+
+It's hard to reliably detect AMSB files. If you feed **listamsb** an
+Atari BASIC file, you'll get gibberish output.
 
 EXIT STATUS
 ===========