more security information in man page, -t option (thanks silt)

peek/peek.1

@@ -43,6 +43,10 @@ The
 .B -p
 option is provided as a convenience and to avoid potential insecure programmer
 error in scripts.
+.PP
+The
+.B -t
+option makes peek exit if not run in a terminal.
 
 .SH DIAGNOSTICS
 
@@ -51,13 +55,21 @@ sysexits(3) if it encounters an error.
 
 .SH BUGS
 
-Accepting secrets in shell scripts is not adviseable.
+Accepting secrets in shell scripts is not adviseable in any context.
 .PP
 The user's environment passed through to the program used with the
 .B -p
 option and their PATH environment variable is used to locate the program.
 If used in a safety-critical application it must be ensured that the
-environment with which peek is used is not compromised.
+environment with which peek is used is not compromised. For example, using
+POSIX env(1) to set a known, safe PATH, and htpasswd(1) from Apache's utilities
+package to hash the input with bcrypt:
+.PP
+.R env -i PATH=/usr/bin peek -1p htpasswd -nBi '' | cut -d : -f 2
+.PP
+On systems that support it, the ioctl(2) command TIOCSTI can be used to insert
+characters into the standard input going to peek. This doesn't allow snooping
+but can be used for general mischief.
 
 .SH COPYRIGHT
 
@@ -65,4 +77,4 @@ Public domain.
 
 .SH SEE ALSO
 
-env(1), read(1), sh(1)
+env(1), ioctl(2), ioctl_tty(2), read(1), sh(1)

peek/peek.c

@@ -6,8 +6,9 @@
 #	include <sysexits.h>
 #endif
 #include <termios.h> /* tcgetattr(3), tcsetattr(3), struct termios, ECHO */
-#include <unistd.h> /* dup(2), execvp(3), fork(2), getopt(3), pipe(2),
+#include <unistd.h> /* dup(2), execvp(3), fork(2), getopt(3), isatty(3),
-                     * write(2), STDERR_FILENO, STDOUT_FILENO */
+                     * pipe(2), write(2), STDERR_FILENO, STDIN_FILENO,
+                     * STDOUT_FILENO */
 
 static char *program_name = "peek";
 
@@ -30,7 +31,7 @@ int main(int argc, char *argv[]){
 
 	eof = EOF;
 	include_eof = 0;
-	while((c = getopt(argc, argv, "1enop")) != -1)
+	while((c = getopt(argc, argv, "1enopt")) != -1)
 		switch(c){
 		case '1': eof = '\n';                 break;
 		case 'n': include_eof = 1;            break;
@@ -42,6 +43,12 @@ int main(int argc, char *argv[]){
 			else
 				outputs[2] = p[1];
 			break;
+		case 't':
+			if(isatty(STDIN_FILENO) != 1){
+				fprintf(stderr, "%s: Must be run in a terminal"
+					" (option -t specified)\n", argv[0]);
+				return EX_USAGE;
+			}
 		default:  goto usage;
 		}