Switch the default pager from "more -s" to "less".

POSIX explicitly allows using a different default pager if that is
documented.  Nowadays, the pager provided in most operating systems
is less(1).  Our man(1) implementation uses less(1) features that
traditional more(1) did not provide, in particular tagging.  Besides,
as noted by deraadt@, the user interface of less(1) is slightly
more refined and preferable over the user inferface of more(1).
This switch was originally suggested by Ian Ropers.

In ./configure, test whether less(1) is available.  If not, fall
back to more(1).  In ./configure.local, support overriding the
automatic test by setting BINM_PAGER.

As explained by jmc@ and deraadt@, the -s flag was added a very
long time ago when an antique version of groff(1) had an annoying
bug in terminal output that would randomly display blank lines in
the middle of pages.  Clearly, -s has no longer been needed for
many years, so drop it from the default pager invocation.

OK deraadt@ jmc@ martijn@ job@ on the OpenBSD version of this patch.

6 files changed, 43 insertions, 20 deletions

diff --git a/apropos.1 b/apropos.1
index 038db46b..c5c90d30 100644
--- a/apropos.1
+++ b/apropos.1
@@ -73,7 +73,7 @@ would.
 If the standard output is a terminal device and
 .Fl c
 is not specified, use
-.Xr more 1
+.Xr less 1
 to paginate them.
 In
 .Fl a
@@ -340,7 +340,7 @@ types appearing in function arguments in the SYNOPSIS
 Any non-empty value of the environment variable
 .Ev MANPAGER
 is used instead of the standard pagination program,
-.Xr more 1 ;
+.Xr less 1 ;
 see
 .Xr man 1
 for details.
@@ -363,8 +363,7 @@ Specifies the pagination program to use when
 .Ev MANPAGER
 is not defined.
 If neither PAGER nor MANPAGER is defined,
-.Xr more 1
-.Fl s
+.Xr less 1
 is used.
 Only used if
 .Fl a
diff --git a/configure b/configure
index 6f77484b..1072a305 100755
--- a/configure
+++ b/configure
@@ -119,6 +119,7 @@ BINM_MAKEWHATIS="makewhatis"
 BINM_MAN="man"
 BINM_SOELIM="soelim"
 BINM_WHATIS="whatis"
+BINM_PAGER=
 MANM_MAN="man"
 MANM_MANCONF="man.conf"
 MANM_MDOC="mdoc"
@@ -343,18 +344,34 @@ else
 	runtest fts FTS || true
 fi
 
+# --- pager ---
+manual=
+if [ -n "${BINM_PAGER}" ]; then
+	manual=" (manual)"
+elif less test-noop.c 1>/dev/null 2>&3; then
+	BINM_PAGER=less
+	echo "tested less: yes" 1>&2
+	echo "tested less: yes" 1>&3
+else
+	BINM_PAGER=more
+	echo "tested less: no" 1>&2
+	echo "tested less: no" 1>&3
+fi
+echo "selected BINM_PAGER=${BINM_PAGER}${manual}" 1>&2
+echo "selected BINM_PAGER=${BINM_PAGER}${manual}" 1>&3
+
 # --- tagging support in the pager ---
-if ismanual "less -T" LESS_T ${HAVE_LESS_T}; then
+if ismanual "${BINM_PAGER} -T" LESS_T ${HAVE_LESS_T}; then
 	:
-elif less -ET /dev/null test-noop.c 1>/dev/null 2>&3; then
+elif ${BINM_PAGER} -T /dev/null test-noop.c 1>/dev/null 2>&3; then
 	HAVE_LESS_T=1
-	echo "tested less -T: yes" 1>&2
-	echo "tested less -T: yes" 1>&3
+	echo "tested ${BINM_PAGER} -T: yes" 1>&2
+	echo "tested ${BINM_PAGER} -T: yes" 1>&3
 	echo 1>&3
 else
 	HAVE_LESS_T=0
-	echo "tested less -T: no" 1>&2
-	echo "tested less -T: no" 1>&3
+	echo "tested ${BINM_PAGER} -T: no" 1>&2
+	echo "tested ${BINM_PAGER} -T: no" 1>&3
 	echo 1>&3
 fi
 
@@ -493,6 +510,7 @@ cat << __HEREDOC__
 #define BINM_MAN "${BINM_MAN}"
 #define BINM_SOELIM "${BINM_SOELIM}"
 #define BINM_WHATIS "${BINM_WHATIS}"
+#define BINM_PAGER "${BINM_PAGER}"
 
 __HEREDOC__
 
diff --git a/configure.local.example b/configure.local.example
index f9d39200..95759f61 100644
--- a/configure.local.example
+++ b/configure.local.example
@@ -151,6 +151,14 @@ BINM_WHATIS=mwhatis		# default is "whatis"
 BINM_MAKEWHATIS=mandocdb	# default is "makewhatis"
 BINM_SOELIM=msoelim		# default is "soelim"
 
+# If less(1) is available, it is used as the default manual pager.
+# Otherwise, more(1) is used: its existence is required by POSIX.
+# It is possible to force using a different default pager, either
+# by giving the name of a program found in the PATH, or by giving
+# an absolute path.
+
+BINM_PAGER=pg			# default is "less" or "more"
+
 # Some distributions do not want hardlinks
 # between installed binary programs.
 # Set the following variable to use symbolic links instead.
diff --git a/main.c b/main.c
index 5fbac335..33e921d0 100644
--- a/main.c
+++ b/main.c
@@ -1218,7 +1218,7 @@ spawn_pager(struct outstate *outst, char *tag_target)
 	if (pager == NULL || *pager == '\0')
 		pager = getenv("PAGER");
 	if (pager == NULL || *pager == '\0')
-		pager = "more -s";
+		pager = BINM_PAGER;
 	cp = mandoc_strdup(pager);
 
 	/*
diff --git a/man.1 b/man.1
index f49369d9..272da822 100644
--- a/man.1
+++ b/man.1
@@ -74,7 +74,7 @@ See
 for a description of the contents of this file.
 .It Fl c
 Copy the manual page to the standard output instead of using
-.Xr more 1
+.Xr less 1
 to paginate it.
 This is done by default if the standard output is not a terminal device.
 .Pp
@@ -275,7 +275,7 @@ is case insensitive.
 Any non-empty value of the environment variable
 .Ev MANPAGER
 is used instead of the standard pagination program,
-.Xr more 1 .
+.Xr less 1 .
 If
 .Xr less 1
 is used, the interactive
@@ -329,8 +329,7 @@ Specifies the pagination program to use when
 .Ev MANPAGER
 is not defined.
 If neither PAGER nor MANPAGER is defined,
-.Xr more 1
-.Fl s
+.Xr less 1
 is used.
 .El
 .Sh FILES
diff --git a/mandoc.1 b/mandoc.1
index 743f0795..cc365e26 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -52,13 +52,13 @@ The options are as follows:
 If the standard output is a terminal device and
 .Fl c
 is not specified, use
-.Xr more 1
+.Xr less 1
 to paginate the output, just like
 .Xr man 1
 would.
 .It Fl c
 Copy the formatted manual pages to the standard output without using
-.Xr more 1
+.Xr less 1
 to paginate them.
 This is the default.
 It can be specified to override
@@ -650,7 +650,7 @@ It never affects the interpretation of input files.
 Any non-empty value of the environment variable
 .Ev MANPAGER
 is used instead of the standard pagination program,
-.Xr more 1 ;
+.Xr less 1 ;
 see
 .Xr man 1
 for details.
@@ -664,8 +664,7 @@ Specifies the pagination program to use when
 .Ev MANPAGER
 is not defined.
 If neither PAGER nor MANPAGER is defined,
-.Xr more 1
-.Fl s
+.Xr less 1
 is used.
 Only used if
 .Fl a