mscan: spawn a pager for interactive use

Makefile

@@ -25,6 +25,7 @@ maddr magrep mexport mflag mgenmid mhdr mlist mpick mscan msed mseq mshow msort
 maddr magrep mhdr mpick mscan mshow : rfc2047.o
 magrep mshow : rfc2045.o
 mshow : filter.o safe_u8putstr.o rfc2231.o pipeto.o
+mscan : pipeto.o
 msort : mystrverscmp.o
 mmime : slurp.o
 

man/mscan.1

@@ -22,7 +22,8 @@ If no
 are passed,
 .Nm
 reads file names from standard input,
-or uses the mails in the current sequence when used interactively.
+or uses the mails in the current sequence when used interactively
+(using a pager).
 .Pp
 By default,
 .Ar format
@@ -166,6 +167,17 @@ You are in
 You are in
 .Sq Li "Resent-To:" .
 .El
+.Sh ENVIRONMENT
+.Bl -tag -width MBLAZE_PAGER
+.It Ev MBLAZE_PAGER
+Any non-empty value of the environment variable
+.Ev MBLAZE_PAGER
+is used instead of the standard pagination program, specified in
+.Ev PAGER .
+When empty or set to
+.Sq Ic cat ,
+no pager is spawned.
+.El
 .Sh EXIT STATUS
 .Ex -std
 .Sh SEE ALSO

mscan.c

@@ -488,6 +488,8 @@ oneline(char *file)
 int
 main(int argc, char *argv[])
 {
+	pid_t pid1 = -1;
+
 	int c;
 	while ((c = getopt(argc, argv, "If:n")) != -1)
 		switch(c) {
@@ -516,8 +518,21 @@ main(int argc, char *argv[])
 		replacement = 0xfffd;
 
 	struct winsize w;
-	if (ioctl(1, TIOCGWINSZ, &w) == 0)
+	if (ioctl(1, TIOCGWINSZ, &w) == 0) {
 		cols = w.ws_col;
+
+		char *pg;
+		pg = getenv("MBLAZE_PAGER");
+		if (!pg)
+			pg = getenv("PAGER");
+		if (pg && *pg && strcmp(pg, "cat") != 0) {
+			pid1 = pipeto(pg);
+			if (pid1 < 0)
+				fprintf(stderr,
+				    "mscan: spawning pager '%s': %s\n",
+				    pg, strerror(errno));
+		}
+	}
 	if (getenv("COLUMNS"))
 		cols = atoi(getenv("COLUMNS"));
 	if (cols <= 40)
@@ -550,5 +565,8 @@ main(int argc, char *argv[])
 		i = blaze822_loop(argc-optind, argv+optind, oneline);
 	fprintf(stderr, "%ld mails scanned\n", i);
 
+	if (pid1 > 0)
+		pipeclose(pid1);
+
 	return 0;
 }