[PATCH 5/6] am: Fix launching of pager

[Jonathan Nieder <jrnieder@gmail.com>]

The git_pager() function used in git am has some problems:

 - It does not check if stdout is a tty, so it always paginates.

 - If $GIT_PAGER uses any environment variables, they are being
   ignored, since it does not run $GIT_PAGER through eval.

Fix them.  While at it, move the definition of git_pager() to
git-sh-setup so authors of other commands are not tempted to
reimplement it with the same mistakes.

If GIT_PAGER is set to the empty string, pagination is disabled.  This
is different from the treatment of GIT_EDITOR by git_editor(), but
consistency with the use of GIT_PAGER by git builtins is more
important.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 git-am.sh       |    5 +----
 git-sh-setup.sh |   16 ++++++++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/git-am.sh b/git-am.sh
index 3c08d53..b11af03 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -663,10 +663,7 @@ do
 		[eE]*) git_editor "$dotest/final-commit"
 		       action=again ;;
 		[vV]*) action=again
-		       : ${GIT_PAGER=$(git var GIT_PAGER)}
-		       : ${LESS=-FRSX}
-		       export LESS
-		       $GIT_PAGER "$dotest/patch" ;;
+		       git_pager "$dotest/patch" ;;
 		*)     action=again ;;
 		esac
 	    done
diff --git a/git-sh-setup.sh b/git-sh-setup.sh
index d56426d..f3b5237 100755
--- a/git-sh-setup.sh
+++ b/git-sh-setup.sh
@@ -107,6 +107,22 @@ git_editor() {
 	eval "$GIT_EDITOR" '"$@"'
 }
 
+git_pager() {
+	if test -z "${GIT_PAGER+set}"
+	then
+		if tty <&1 >/dev/null 2>/dev/null
+		then
+			GIT_PAGER=cat
+		else
+			GIT_PAGER=$(git var GIT_PAGER)
+		fi
+	fi
+	: ${LESS=-FRSX}
+	export LESS
+
+	eval "$GIT_PAGER" '"$@"'
+}
+
 sane_grep () {
 	GREP_OPTIONS= LC_ALL=C grep "$@"
 }
-- 
1.7.0