pidof: allow to suppress output

Often pidof is used in shell scripts in this form:

    if pidof daemon >/dev/null; then
        ...
    fi

The redirection to /dev/null is needed because otherwise the script
would output the found PIDs.
Let's add a -q option which, similary to grep, just sets the exit code.
Also exit on first match, as there is no reason to proceed further when
at least a process is matched.

Tested with:

    $ ./pidof bash
    17701 14019 5276 2967
    $ echo $?
    0
    $ ./pidof bashx
    $ echo $?
    1
    $ ./pidof -q bash
    $ echo $?
    0
    $ ./pidof -q bashx
    $ echo $?
    1

diff --git a/pidof.1 b/pidof.1
index 5ed61cdd9b6b1c29d255356c8d4abfd756f488fd..9fb4df7468de774079185ebeecea6bd5a0746ff5 100644 (file)
--- a/pidof.1
+++ b/pidof.1
@@ -15,17 +15,17 @@
 .\" along with this program; if not, write to the Free Software
 .\" Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 .\"
-.TH PIDOF 1 "2020-06-04" "" "User Commands"
+.TH PIDOF 1 "2020-12-22" "" "User Commands"
 .SH NAME
 pidof -- find the process ID of a running program
 .SH SYNOPSIS
 .B pidof
 .RB [ \-s ]
 .RB [ \-c ]
+.RB [ \-q ]
+.RB [ \-w ]
 .RB [ \-x ]
 .RB [ \-o
-.IR omitpid[,omitpid...] ]
-.RB [ \-o
 .IR omitpid[,omitpid...]... ]
 .RB [ \-S
 .IR separator ]
@@ -42,12 +42,14 @@ Single shot - this instructs the program to only return one \fIpid\fP.
 Only return process ids that are running with the same root directory.
 This option is ignored for non-root users, as they will be unable to check
 the current root directory of processes they do not own.
-.IP \-x
-Scripts too - this causes the program to also return process id's of
-shells running the named scripts.
+.IP \-q
+Quiet mode, suppress any output and only sets the exit status accordingly.
 .IP \-w
 Show also processes that do not have visible command line (e.g. kernel
 worker threads).
+.IP \-x
+Scripts too - this causes the program to also return process id's of
+shells running the named scripts.
 .IP "-o \fIomitpid\fP"
 Tells \fIpidof\fP to omit processes with that process id. The special
 pid \fB%PPID\fP can be used to name the parent process of the \fIpidof\fP

diff --git a/pidof.c b/pidof.c
index 25824e938404760d36ae45b82695a65de963a90f..1d30c245f40c1969faf0b41c8c4c942101e0c667 100644 (file)
--- a/pidof.c
+++ b/pidof.c
@@ -56,7 +56,7 @@ static int opt_single_shot    = 0;  /* -s */
 static int opt_scripts_too    = 0;  /* -x */
 static int opt_rootdir_check  = 0;  /* -c */
 static int opt_with_workers   = 0;  /* -w */
-
+static int opt_quiet          = 0;  /* -q */
 
 static char *pidof_root = NULL;
 
@@ -70,8 +70,9 @@ static int __attribute__ ((__noreturn__)) usage(int opt)
        fputs(USAGE_OPTIONS, fp);
        fputs(_(" -s, --single-shot         return one PID only\n"), fp);
        fputs(_(" -c, --check-root          omit processes with different root\n"), fp);
-       fputs(_(" -x                        also find shells running the named scripts\n"), fp);
+       fputs(_(" -q,                       quiet mode, only set the exit code\n"), fp);
        fputs(_(" -w, --with-workers        show kernel workers too\n"), fp);
+       fputs(_(" -x                        also find shells running the named scripts\n"), fp);
        fputs(_(" -o, --omit-pid <PID,...>  omit processes with PID\n"), fp);
        fputs(_(" -S, --separator SEP       use SEP as separator put between PIDs"), fp);
        fputs(USAGE_SEPARATOR, fp);
@@ -294,13 +295,14 @@ int main (int argc, char **argv)
        int first_pid = 1;
 
        const char *separator = " ";
-       const char *opts = "scnxwmo:S:?Vh";
+       const char *opts = "scnqxwmo:S:?Vh";
 
        static const struct option longopts[] = {
                {"check-root", no_argument, NULL, 'c'},
                {"single-shot", no_argument, NULL, 's'},
                {"omit-pid", required_argument, NULL, 'o'},
                {"separator", required_argument, NULL, 'S'},
+               {"quiet", no_argument, NULL, 'q'},
                {"with-workers", no_argument, NULL, 'w'},
                {"help", no_argument, NULL, 'h'},
                {"version", no_argument, NULL, 'V'},
@@ -318,6 +320,9 @@ int main (int argc, char **argv)
        /* process command-line options */
        while ((opt = getopt_long (argc, argv, opts, longopts, NULL)) != -1) {
                switch (opt) {
+               case 'q':
+                       opt_quiet = 1;
+                       /* fallthrough */
                case 's':
                        opt_single_shot = 1;
                        break;
@@ -372,11 +377,13 @@ int main (int argc, char **argv)
 
                        found = 1;
                        for (i = proc_count - 1; i >= 0; i--) { /* and display their PIDs */
-                               if (first_pid) {
-                                       first_pid = 0;
-                                       printf ("%ld", (long) procs[i].pid);
-                               } else {
-                                       printf ("%s%ld", separator, (long) procs[i].pid);
+                               if (!opt_quiet) {
+                                       if (first_pid) {
+                                               first_pid = 0;
+                                               printf ("%ld", (long) procs[i].pid);
+                                       } else {
+                                               printf ("%s%ld", separator, (long) procs[i].pid);
+                                       }
                                }
                                if (opt_single_shot) break;
                        }
@@ -386,7 +393,7 @@ int main (int argc, char **argv)
        }
 
        /* final line feed */
-       if (found) printf("\n");
+       if (!opt_quiet && found) printf("\n");
 
        /* some cleaning */
        safe_free(procs);