grep: add -H flag

grep.1

@@ -3,7 +3,7 @@
 grep \- search files for a pattern
 .SH SYNOPSIS
 .B grep
-.RB [ \-Ecilnqv ]
+.RB [ \-EHcilnqv ]
 .RB [ \-e
 .I pattern ]
 .I pattern
@@ -24,6 +24,10 @@ status code is 2.
 .B \-E
 matches using extended regex.
 .TP
+.B \-H
+prefixes each matching line with its filename in the output. This is the
+default when there is more than one file specified.
+.TP
 .B \-c
 prints only a count of matching lines.
 .TP

grep.c

@@ -15,6 +15,7 @@ static int grep(FILE *, const char *);
 
 static int eflag = 0;
 static int vflag = 0;
+static int Hflag = 0;
 static int many;
 static char mode = 0;
 
@@ -27,7 +28,7 @@ static struct plist {
 static void
 usage(void)
 {
-	enprintf(Error, "usage: %s [-Ecilnqv] [-e pattern] pattern [files...]\n", argv0);
+	enprintf(Error, "usage: %s [-EHcilnqv] [-e pattern] pattern [files...]\n", argv0);
 }
 
 int
@@ -42,6 +43,9 @@ main(int argc, char *argv[])
 	case 'E':
 		flags |= REG_EXTENDED;
 		break;
+	case 'H':
+		Hflag = 1;
+		break;
 	case 'e':
 		addpattern(EARGF(usage()));
 		eflag = 1;
@@ -143,7 +147,7 @@ grep(FILE *fp, const char *str)
 			case 'q':
 				exit(Match);
 			default:
-				if (many)
+				if (many || Hflag)
 					printf("%s:", str);
 				if (mode == 'n')
 					printf("%ld:", n);