From: Nicholas Clark <nick@ccl4.org>
Date: Mon, 31 May 2010 10:47:04 +0000 (+0100)
Subject: Reorder the entry for die, moving discussion of the exit code later.
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=4c050ad563ece4467b3b083d8efcf2b62ad0b9c5;p=p5sagit%2Fp5-mst-13.2.git

Reorder the entry for die, moving discussion of the exit code later.

Change to start with "C<die> raises an exception." and phrase in terms of
handling exceptions, and then how uncaught exceptions result in process exit.
Do not give details of the exit code in the first paragraph. Move this to a
later paragraph, clarify that $! is often unpredictable, and stress that 255
is the last resort exit code.
---

diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod
index 76bf048..ccffcdb 100644
--- a/pod/perlfunc.pod
+++ b/pod/perlfunc.pod
@@ -1263,13 +1263,11 @@ final operation is an element or slice of an aggregate:
 =item die LIST
 X<die> X<throw> X<exception> X<raise> X<$@> X<abort>
 
-Outside an C<eval>, prints the value of LIST to C<STDERR> and
-exits with the current value of C<$!> (errno).  If C<$!> is C<0>,
-exits with the value of C<<< ($? >> 8) >>> (backtick `command`
-status).  If C<<< ($? >> 8) >>> is C<0>, exits with C<255>.  Inside
-an C<eval(),> the error message is stuffed into C<$@> and the
-C<eval> is terminated with the undefined value.  This makes
-C<die> the way to raise an exception.
+C<die> raises an exception. Inside an C<eval> the error message is stuffed
+into C<$@> and the C<eval> is terminated with the undefined value.
+If the exception is outside of all enclosing C<eval>s, then the uncaught
+exception prints LIST to C<STDERR> and exits with a non-zero value. If you
+need to exit the process with a specific exit code, see L<exit>.
 
 Equivalent examples:
 
@@ -1295,8 +1293,6 @@ produce, respectively
     /etc/games is no good at canasta line 123.
     /etc/games is no good, stopped at canasta line 123.
 
-See also exit(), warn(), and the Carp module.
-
 If the output is empty and C<$@> already contains a value (typically from a
 previous eval) that value is reused after appending C<"\t...propagated">.
 This is useful for propagating exceptions:
@@ -1312,6 +1308,19 @@ were called.
 
 If C<$@> is empty then the string C<"Died"> is used.
 
+If an uncaught exception results in interpreter exit, the exit code is
+determined from the values of C<$!> and C<$?> with this pseudocode:
+
+    exit $! if $!;              # errno
+    exit $? >> 8 if $? >> 8;    # child exit status
+    exit 255;                   # last resort
+
+The intent is to squeeze as much possible information about the likely cause
+into the limited space of the system exit code. However, as C<$!> is the value
+of C's C<errno>, which can be set by any system call, this means that the value
+of the exit code used by C<die> can be non-predictable, so should not be relied
+upon, other than to be non-zero.
+
 You can also call C<die> with a reference argument, and if this is trapped
 within an C<eval>, C<$@> contains that reference.  This permits more
 elaborate exception handling using objects that maintain arbitrary state
@@ -1355,6 +1364,8 @@ as the first line of the handler (see L<perlvar/$^S>).  Because
 this promotes strange action at a distance, this counterintuitive
 behavior may be fixed in a future release.
 
+See also exit(), warn(), and the Carp module.
+
 =item do BLOCK
 X<do> X<block>