[PATCH] kill: with -l,-t list signal 0

[Pádraig Brady]

The 0 (EXIT) signal is valid as input
(and useful to determine existence of a pid),
so list it along with other signals.

* src/kill.c (list_signals): Start loops at 0, not 1.
* tests/misc/kill.sh: Add a test case.
* NEWS: Mention the change in behavior.
---
 NEWS               | 2 ++
 src/kill.c         | 6 +++---
 tests/misc/kill.sh | 3 +++
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/NEWS b/NEWS
index 9c6f2fb0d..f76393506 100644
--- a/NEWS
+++ b/NEWS
@@ -46,6 +46,8 @@ GNU coreutils NEWS                                    -*- 
outline -*-
   install -C now dereferences symlink sources when comparing,
   rather than always treating as different and performing the copy.
 
+  kill -l and -t now list signal 0, as it's a valid signal to send.
+
   ls's -f option now simply acts like -aU, instead of also ignoring
   some earlier options.  For example 'ls -fl' and 'ls -lf' are now
   equivalent because -f no longer ignores an earlier -l.  The new
diff --git a/src/kill.c b/src/kill.c
index 8b9a2650f..314855653 100644
--- a/src/kill.c
+++ b/src/kill.c
@@ -120,7 +120,7 @@ list_signals (bool table, char *const *argv)
         num_width++;
 
       /* Compute the maximum width of a signal name.  */
-      for (signum = 1; signum <= SIGNUM_BOUND; signum++)
+      for (signum = 0; signum <= SIGNUM_BOUND; signum++)
         if (sig2str (signum, signame) == 0)
           {
             idx_t len = strlen (signame);
@@ -142,7 +142,7 @@ list_signals (bool table, char *const *argv)
               }
           }
       else
-        for (signum = 1; signum <= SIGNUM_BOUND; signum++)
+        for (signum = 0; signum <= SIGNUM_BOUND; signum++)
           if (sig2str (signum, signame) == 0)
             print_table_row (num_width, signum, name_width, signame);
     }
@@ -165,7 +165,7 @@ list_signals (bool table, char *const *argv)
               printf ("%d\n", signum);
           }
       else
-        for (signum = 1; signum <= SIGNUM_BOUND; signum++)
+        for (signum = 0; signum <= SIGNUM_BOUND; signum++)
           if (sig2str (signum, signame) == 0)
             puts (signame);
     }
diff --git a/tests/misc/kill.sh b/tests/misc/kill.sh
index 82812eada..ed4773f65 100755
--- a/tests/misc/kill.sh
+++ b/tests/misc/kill.sh
@@ -68,4 +68,7 @@ test -n "$SIG_SEQ" || framework_failure_
 env kill -l -- $SIG_SEQ || fail=1
 env kill -t -- $SIG_SEQ || fail=1
 
+# Verify first signal number listed is 0
+test $(env kill -l $(env kill -l | head -n1)) = 0 || fail=1
+
 Exit $fail
-- 
2.47.1