Provide a build time default-pager setting

Provide a DEFAULT_PAGER knob so packagers can set the fallback
pager to something appropriate during the build.

Examples:

On (old) solaris systems, /usr/bin/less (typically the first less
found) doesn't understand the default arguments (FXRS), which
forces users to alter their environment (PATH, GIT_PAGER, LESS,
etc) or have a local or global gitconfig before paging works as
expected.

On Debian systems, by policy packages must fall back to the
'pager' command, so that changing the target of the
/usr/bin/pager symlink changes the default pager for all packages
at once.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -201,6 +201,10 @@ all::
 #
 # Define NO_REGEX if you have no or inferior regex support in your C library.
 #
+# Define DEFAULT_PAGER to a sensible pager command (defaults to "less") if
+# you want to use something different.  The value will be interpreted by the
+# shell at runtime when it is used.
+#
 # Define DEFAULT_EDITOR to a sensible editor command (defaults to "vi") if you
 # want to use something different.  The value will be interpreted by the shell
 # if necessary when it is used.  Examples:
@@ -1380,6 +1384,13 @@ DEFAULT_EDITOR_CQ_SQ = $(subst ','\'',$(DEFAULT_EDITOR_CQ))
 BASIC_CFLAGS += -DDEFAULT_EDITOR='$(DEFAULT_EDITOR_CQ_SQ)'
 endif
 
+ifdef DEFAULT_PAGER
+DEFAULT_PAGER_CQ = "$(subst ",\",$(subst \,\\,$(DEFAULT_PAGER)))"
+DEFAULT_PAGER_CQ_SQ = $(subst ','\'',$(DEFAULT_PAGER_CQ))
+
+BASIC_CFLAGS += -DDEFAULT_PAGER='$(DEFAULT_PAGER_CQ_SQ)'
+endif
+
 ALL_CFLAGS += $(BASIC_CFLAGS)
 ALL_LDFLAGS += $(BASIC_LDFLAGS)
 

pager.c

@@ -2,6 +2,10 @@
 #include "run-command.h"
 #include "sigchain.h"
 
+#ifndef DEFAULT_PAGER
+#define DEFAULT_PAGER "less"
+#endif
+
 /*
  * This is split up from the rest of git so that we can do
  * something different on Windows.
@@ -60,7 +64,7 @@ const char *git_pager(void)
 	if (!pager)
 		pager = getenv("PAGER");
 	if (!pager)
-		pager = "less";
+		pager = DEFAULT_PAGER;
 	else if (!*pager || !strcmp(pager, "cat"))
 		pager = NULL;