[systemd-devel] [PATCH] systemctl: implement auto-pager a la git

[Miklos Vajna]

---

Hi,

I hope the subjects describes the patch enough - though I would like to
point out one detail. I guess there can be great flames about the
default value of LESS if it's unset - I took FRSX as that's what git
uses right now.

 TODO              |    2 --
 man/systemctl.xml |    7 +++++++
 src/systemctl.c   |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/TODO b/TODO
index 21f06a6..c9a7617 100644
--- a/TODO
+++ b/TODO
@@ -67,8 +67,6 @@
 
 * suspend, resume
 
-* systemctl auto-pager a la git
-
 * readahead: btrfs/LVM SSD detection
 
 * when processes remain in a service even though the start command failed enter active
diff --git a/man/systemctl.xml b/man/systemctl.xml
index 6b05e95..c21ed85 100644
--- a/man/systemctl.xml
+++ b/man/systemctl.xml
@@ -171,6 +171,13 @@
                                 enqueued.</para></listitem> </varlistentry>
 
                         <varlistentry>
+                                <term><option>--no-pager</option></term>
+
+				<listitem><para>Do not pipe output into a
+				pager.</para></listitem>
+			</varlistentry>
+
+                        <varlistentry>
                                 <term><option>--system</option></term>
 
                                 <listitem><para>Talk to the systemd
diff --git a/src/systemctl.c b/src/systemctl.c
index 4768fb2..585f1dc 100644
--- a/src/systemctl.c
+++ b/src/systemctl.c
@@ -65,6 +65,7 @@ static bool arg_user = false;
 static bool arg_global = false;
 static bool arg_immediate = false;
 static bool arg_no_block = false;
+static bool arg_no_pager = false;
 static bool arg_no_wtmp = false;
 static bool arg_no_sync = false;
 static bool arg_no_wall = false;
@@ -4110,6 +4111,7 @@ static int systemctl_help(void) {
                "                      pending\n"
                "  -q --quiet          Suppress output\n"
                "     --no-block       Do not wait until operation finished\n"
+               "     --no-pager       Do not pipe output into a pager.\n"
                "     --system         Connect to system manager\n"
                "     --user           Connect to user service manager\n"
                "     --order          When generating graph for dot, show only order\n"
@@ -4249,6 +4251,7 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
                 ARG_SYSTEM,
                 ARG_GLOBAL,
                 ARG_NO_BLOCK,
+		ARG_NO_PAGER,
                 ARG_NO_WALL,
                 ARG_ORDER,
                 ARG_REQUIRE,
@@ -4272,6 +4275,7 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
                 { "system",    no_argument,       NULL, ARG_SYSTEM    },
                 { "global",    no_argument,       NULL, ARG_GLOBAL    },
                 { "no-block",  no_argument,       NULL, ARG_NO_BLOCK  },
+                { "no-pager",  no_argument,       NULL, ARG_NO_PAGER  },
                 { "no-wall",   no_argument,       NULL, ARG_NO_WALL   },
                 { "quiet",     no_argument,       NULL, 'q'           },
                 { "order",     no_argument,       NULL, ARG_ORDER     },
@@ -4348,6 +4352,10 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
                         arg_no_block = true;
                         break;
 
+		case ARG_NO_PAGER:
+			arg_no_pager = true;
+			break;
+
                 case ARG_NO_WALL:
                         arg_no_wall = true;
                         break;
@@ -5274,6 +5282,48 @@ static int runlevel_main(void) {
         return 0;
 }
 
+static void pager_open(void) {
+	pid_t pid;
+	int fd[2];
+	const char *pager = getenv("PAGER");
+
+	if (!on_tty() || arg_no_pager)
+		return;
+	if (!pager)
+		pager = "less";
+	else if (!*pager || !strcmp(pager, "cat"))
+		return;
+
+	if (pipe(fd) < 0)
+		return;
+	pid = fork();
+	if (pid < 0) {
+		close(fd[0]);
+		close(fd[1]);
+		return;
+	}
+
+	/* Return in the child */
+	if (!pid) {
+		dup2(fd[1], 1);
+		close(fd[0]);
+		close(fd[1]);
+		return;
+	}
+
+	/* The original process turns into the PAGER */
+	dup2(fd[0], 0);
+	close(fd[0]);
+	close(fd[1]);
+
+	setenv("LESS", "FRSX", 0);
+	execlp(pager, pager, NULL);
+	execl("/bin/sh", "sh", "-c", pager, NULL);
+
+	log_error("unable to execute pager '%s'", pager);
+	_exit(EXIT_FAILURE);
+}
+
 int main(int argc, char*argv[]) {
         int r, retval = EXIT_FAILURE;
         DBusConnection *bus = NULL;
@@ -5291,6 +5341,8 @@ int main(int argc, char*argv[]) {
                 goto finish;
         }
 
+	pager_open();
+
         /* /sbin/runlevel doesn't need to communicate via D-Bus, so
          * let's shortcut this */
         if (arg_action == ACTION_RUNLEVEL) {
-- 
1.7.3.2.164.g6f10c.dirty