? cat-date.c
Index: cat.1
===================================================================
RCS file: /home/ncvs/src/bin/cat/cat.1,v
retrieving revision 1.25
diff -u -r1.25 cat.1
--- cat.1	16 Jan 2005 16:41:55 -0000	1.25
+++ cat.1	6 Sep 2006 20:34:17 -0000
@@ -32,7 +32,7 @@
 .\"     @(#)cat.1	8.3 (Berkeley) 5/2/95
 .\" $FreeBSD: src/bin/cat/cat.1,v 1.25 2005/01/16 16:41:55 ru Exp $
 .\"
-.Dd March 21, 2004
+.Dd September 6, 2006
 .Dt CAT 1
 .Os
 .Sh NAME
@@ -41,6 +41,7 @@
 .Sh SYNOPSIS
 .Nm
 .Op Fl benstuv
+.Op Fl D Ar date_format
 .Op Ar
 .Sh DESCRIPTION
 The
@@ -73,6 +74,31 @@
 .Bl -tag -width indent
 .It Fl b
 Number the non-blank output lines, starting at 1.
+.It Fl D Ar date_format
+Prefix each output line with a string that indicates the date and/or
+time when that line was read by the
+.Nm
+utility.
+The resolution used for that time will be to the nearest second.
+The format of that prefix is specified by the value of
+.Ar date_format .
+The
+.Ar date_format
+argument may contain any of the conversion specifications described in the
+.Xr strftime 3
+manual page, as well as any arbitrary text.
+No separator will be inserted between the generated prefix and the
+remainder of the output line, so if a separator is desired then
+the value for
+.Ar date_format
+should end with a space or the conversion specifier of
+.Dq Li %t .
+The
+.Fl t
+and
+.Fl v
+options do not affect any characters generated by the
+.Ar date_format .
 .It Fl e
 Display non-printing characters (see the
 .Fl v
@@ -152,6 +178,24 @@
 when it encountered the first
 .Ql \&-
 operand.
+.Pp
+The command:
+.Pp
+.Dl "command | cat -D '%F %T '"
+.Pp
+will prepend the current date/time in the form
+.Dq Li YYYY-MM-DD HH:MM:SS ,
+followed by a space, to each line of the stdout from
+.Nm command .
+This is useful for timestamping output, especially if
+.Nm command
+will be running for a long period of time, and you want to know when
+each output line was written.
+Note that
+.Nm command
+must have unbuffered or line-buffered output for the
+.Fl D
+option to produce accurate timestamps.
 .Sh SEE ALSO
 .Xr head 1 ,
 .Xr more 1 ,
@@ -160,7 +204,8 @@
 .Xr tail 1 ,
 .Xr vis 1 ,
 .Xr zcat 1 ,
-.Xr setbuf 3
+.Xr setbuf 3 ,
+.Xr strftime 3
 .Rs
 .%A Rob Pike
 .%T "UNIX Style, or cat -v Considered Harmful"
@@ -175,7 +220,7 @@
 specification.
 .Pp
 The flags
-.Op Fl benstv
+.Op Fl bDenstv
 are extensions to the specification.
 .Sh HISTORY
 A
@@ -199,3 +244,9 @@
 or
 .Fl v
 option is in effect.
+.Pp
+The
+.Nm
+utility does not correctly handle multibyte characters in the
+argument to
+.Fl D .
Index: cat.c
===================================================================
RCS file: /home/ncvs/src/bin/cat/cat.c,v
retrieving revision 1.32
diff -u -r1.32 cat.c
--- cat.c	10 Jan 2005 08:39:20 -0000	1.32
+++ cat.c	6 Sep 2006 20:34:17 -0000
@@ -64,13 +64,19 @@
 #include <unistd.h>
 #include <stddef.h>
 
+#define	DATEPFX_MAXLEN	1024
+
 int bflag, eflag, nflag, sflag, tflag, vflag;
 int rval;
+static time_t prev_time;
+static const char *datefmt;
+static char *datepfx;
 const char *filename;
 
 static void usage(void);
 static void scanfiles(char *argv[], int cooked);
 static void cook_cat(FILE *);
+static void set_datepfx(void);
 static void raw_cat(int);
 
 #ifndef NO_UDOM_SUPPORT
@@ -84,11 +90,14 @@
 
 	setlocale(LC_CTYPE, "");
 
-	while ((ch = getopt(argc, argv, "benstuv")) != -1)
+	while ((ch = getopt(argc, argv, "bD:enstuv")) != -1)
 		switch (ch) {
 		case 'b':
 			bflag = nflag = 1;	/* -b implies -n */
 			break;
+		case 'D':
+			datefmt = optarg;
+			break;
 		case 'e':
 			eflag = vflag = 1;	/* -e implies -v */
 			break;
@@ -112,7 +121,17 @@
 		}
 	argv += optind;
 
-	if (bflag || eflag || nflag || sflag || tflag || vflag)
+	/*
+	 * If -D was specified, then make an initial call to set the prefix.
+	 * This means that if the format is likely to generate an error, the
+	 * user will see that error immediately instead of waiting until
+	 * after the first line is read in.
+	 */
+	if (datefmt != NULL)
+		set_datepfx();
+
+	if (bflag || eflag || nflag || sflag || tflag || vflag ||
+		datefmt != NULL)
 		scanfiles(argv, 1);
 	else
 		scanfiles(argv, 0);
@@ -125,7 +144,7 @@
 static void
 usage(void)
 {
-	fprintf(stderr, "usage: cat [-benstuv] [file ...]\n");
+	fprintf(stderr, "usage: cat [-benstuv] [-D datefmt] [file ...]\n");
 	exit(1);
 	/* NOTREACHED */
 }
@@ -198,6 +217,12 @@
 				if (ferror(stdout))
 					break;
 			}
+			if (datefmt != NULL) {
+				set_datepfx();
+				(void)fputs(datepfx, stdout);
+				if (ferror(stdout))
+					break;
+			}
 		}
 		if (ch == '\n') {
 			if (eflag && putchar('$') == EOF)
@@ -261,6 +286,30 @@
 	}
 }
 
+static void
+set_datepfx(void)
+{
+	int reslen;
+	time_t now;
+
+	if (datepfx == NULL)
+		datepfx = malloc(DATEPFX_MAXLEN);
+
+	/*
+	 * Avoid the calls to localtime and strftime if the current second
+	 * is the same as the second when the previous line was read in.
+	 */
+	now = time(NULL);
+	if (now == prev_time)
+		return;
+	prev_time = now;
+
+	reslen = strftime(datepfx, DATEPFX_MAXLEN, datefmt, localtime(&now));
+	if (reslen == 0)
+		errx(1, "Format specified by -D results in prefix > %d bytes.",
+		    DATEPFX_MAXLEN);
+}
+
 #ifndef NO_UDOM_SUPPORT
 
 static int