$shucks++;
die "Somebody sent me a SIG$signame";
}
- $SIG{INT} = __PACKAGE__ . "::catch_zap";
+ $SIG{INT} = __PACKAGE__ . "::catch_zap";
$SIG{INT} = \&catch_zap; # best strategy
Prior to Perl 5.8.0 it was necessary to do as little as you possibly
Sending a signal to a negative process ID means that you send the signal
to the entire Unix process group. This code sends a hang-up signal to all
-processes in the current process group, and also sets $SIG{HUP} to C<"IGNORE">
+processes in the current process group, and also sets $SIG{HUP} to C<"IGNORE">
so it doesn't kill itself:
# block scope for local
{
local $SIG{HUP} = "IGNORE";
- kill HUP => -$$;
- # snazzy writing of: kill("HUP", -$$)
+ kill HUP => -getpgrp();
+ # snazzy writing of: kill("HUP", -getpgrp())
}
Another interesting signal to send is signal number zero. This doesn't
$SIG{CHLD} = sub {
# don't change $! and $? outside handler
local ($!, $?);
- my $pid = waitpid(-1, WNOHANG);
- return if $pid == -1;
- return unless defined $children{$pid};
- delete $children{$pid};
- cleanup_child($pid, $?);
+ while ( (my $pid = waitpid(-1, WNOHANG)) > 0 ) {
+ delete $children{$pid};
+ cleanup_child($pid, $?);
+ }
};
while (1) {
need to do your own fork() and exec(), and kill the errant child process.
For more complex signal handling, you might see the standard POSIX
-module. Lamentably, this is almost entirely undocumented, but
-the F<t/lib/posix.t> file from the Perl source distribution has some
-examples in it.
+module. Lamentably, this is almost entirely undocumented, but the
+F<ext/POSIX/t/sigaction.t> file from the Perl source distribution has
+some examples in it.
=head2 Handling the SIGHUP Signal in Daemons
located in the subroutine C<code()>, which just prints some debugging
info to show that it works; it should be replaced with the real code.
- #!/usr/bin/perl -w
+ #!/usr/bin/perl
+
+ use strict;
+ use warnings;
use POSIX ();
use FindBin ();
use File::Basename ();
- use File::Spec::Functions;
+ use File::Spec::Functions qw(catfile);
$| = 1;
print "PID: $$\n";
print "ARGV: @ARGV\n";
my $count = 0;
- while (++$count) {
+ while (1) {
sleep 2;
- print "$count\n";
+ print ++$count, "\n";
}
}
opcode (e.g. a regular expression operation on a very large string) will
not be seen until the current opcode completes.
-If a signal of any given type fires multiple times during an opcode
+If a signal of any given type fires multiple times during an opcode
(such as from a fine-grained timer), the handler for that signal will
be called only once, after the opcode completes; all other
instances will be discarded. Furthermore, if your system's signal queue
try something like the following:
- use POSIX qw(SIGALRM);
- POSIX::sigaction(SIGALRM, POSIX::SigAction->new(sub { die "alarm" }))
+ use POSIX qw(SIGALRM);
+ POSIX::sigaction(SIGALRM,
+ POSIX::SigAction->new(sub { die "alarm" }))
|| die "Error setting SIGALRM handler: $!\n";
Another way to disable the safe signal behavior locally is to use
SA_RESTART flag when installing %SIG handlers. This meant that
restartable system calls would continue rather than returning when
a signal arrived. In order to deliver deferred signals promptly,
-Perl 5.8.0 and later do I<not> use SA_RESTART. Consequently,
+Perl 5.8.0 and later do I<not> use SA_RESTART. Consequently,
restartable system calls can fail (with $! set to C<EINTR>) in places
where they previously would have succeeded.
The default C<:perlio> layer retries C<read>, C<write>
-and C<close> as described above; interrupted C<wait> and
+and C<close> as described above; interrupted C<wait> and
C<waitpid> calls will always be retried.
=item Signals as "faults"
to handle. Consider:
open(FH, "|bogus") || die "can't fork: $!";
- print FH "bang\n"; # neither necessary nor sufficient
+ print FH "bang\n"; # neither necessary nor sufficient
# to check print retval!
close(FH) || die "can't close: $!";
standard file descriptors from and to F</dev/null> so that random
output doesn't wind up on the user's terminal.
- use POSIX "setsid";
+ use POSIX "setsid";
- sub daemonize {
- chdir("/") || die "can't chdir to /: $!";
- open(STDIN, "< /dev/null") || die "can't read /dev/null: $!";
- open(STDOUT, "> /dev/null") || die "can't write to /dev/null: $!";
- defined(my $pid = fork()) || die "can't fork: $!";
- exit if $pid; # non-zero now means I am the parent
- (setsid() != -1) || die "Can't start a new session: $!";
- open(STDERR, ">&STDOUT") || die "can't dup stdout: $!";
- }
+ sub daemonize {
+ chdir("/") || die "can't chdir to /: $!";
+ open(STDIN, "< /dev/null") || die "can't read /dev/null: $!";
+ open(STDOUT, "> /dev/null") || die "can't write to /dev/null: $!";
+ defined(my $pid = fork()) || die "can't fork: $!";
+ exit if $pid; # non-zero now means I am the parent
+ (setsid() != -1) || die "Can't start a new session: $!";
+ open(STDERR, ">&STDOUT") || die "can't dup stdout: $!";
+ }
The fork() has to come before the setsid() to ensure you aren't a
process group leader; the setsid() will fail if you are. If your
system doesn't have the setsid() function, open F</dev/tty> and use the
C<TIOCNOTTY> ioctl() on it instead. See tty(4) for details.
-Non-Unix users should check their C<< I<Your_OS>::Process >> module for
+Non-Unix users should check their C<< I<Your_OS>::Process >> module for
other possible solutions.
=head2 Safe Pipe Opens
}
} until defined $pid;
- if ($pid) { # I am the parent
+ if ($pid) { # I am the parent
print KID_TO_WRITE @some_data;
close(KID_TO_WRITE) || warn "kid exited $?";
} else { # I am the child
# drop permissions in setuid and/or setgid programs:
- ($EUID, $EGID) = ($UID, $GID);
- open (OUTFILE, "> $PRECIOUS")
+ ($EUID, $EGID) = ($UID, $GID);
+ open (OUTFILE, "> $PRECIOUS")
|| die "can't open $PRECIOUS: $!";
while (<STDIN>) {
print OUTFILE; # child's STDIN is parent's KID_TO_WRITE
}
It is very easy to dead-lock a process using this form of open(), or
-indeed with any use of pipe() with multiple subprocesses. The
+indeed with any use of pipe() with multiple subprocesses. The
example above is "safe" because it is simple and calls exec(). See
L</"Avoiding Pipe Deadlocks"> for general safety principles, but there
are extra gotchas with Safe Pipe Opens.
One would use either of these:
- open(PS_PIPE, "-|", "ps", "aux")
+ open(PS_PIPE, "-|", "ps", "aux")
|| die "can't open ps pipe: $!";
@ps_args = qw[ ps aux ];
Because there are more than three arguments to open(), forks the ps(1)
command I<without> spawning a shell, and reads its standard output via the
C<PS_PIPE> filehandle. The corresponding syntax to I<write> to command
-pipes is to use C<"|-"> in place of C<"-|">.
+pipes is to use C<"|-"> in place of C<"-|">.
This was admittedly a rather silly example, because you're using string
literals whose content is perfectly safe. There is therefore no cause to
=for TODO
Hold on, is this even true? First it says that socketpair() is avoided
-for portability, but then it says it probably won't work except on
+for portability, but then it says it probably won't work except on
Unixy systems anyway. Which one of those is true?
Here's an example of using open2():
reopen the appropriate handles to STDIN and STDOUT and call other processes.
(The following example lacks proper error checking.)
- #!/usr/bin/perl -w
- # pipe1 - bidirectional communication using two pipe pairs
- # designed for the socketpair-challenged
- use IO::Handle; # thousands of lines just for autoflush :-(
- pipe(PARENT_RDR, CHILD_WTR); # XXX: check failure?
- pipe(CHILD_RDR, PARENT_WTR); # XXX: check failure?
- CHILD_WTR->autoflush(1);
- PARENT_WTR->autoflush(1);
-
- if ($pid = fork()) {
- close PARENT_RDR;
- close PARENT_WTR;
- print CHILD_WTR "Parent Pid $$ is sending this\n";
- chomp($line = <CHILD_RDR>);
- print "Parent Pid $$ just read this: '$line'\n";
- close CHILD_RDR; close CHILD_WTR;
- waitpid($pid, 0);
- } else {
- die "cannot fork: $!" unless defined $pid;
- close CHILD_RDR;
- close CHILD_WTR;
-
chomp($line = <PARENT_RDR>);
- print "Child Pid $$ just read this: '$line'\n";
- print PARENT_WTR "Child Pid $$ is sending this\n";
- close PARENT_RDR;
- close PARENT_WTR;
- exit(0);
- }
+ #!/usr/bin/perl -w
+ # pipe1 - bidirectional communication using two pipe pairs
+ # designed for the socketpair-challenged
+ use IO::Handle; # thousands of lines just for autoflush :-(
+ pipe(PARENT_RDR, CHILD_WTR); # XXX: check failure?
+ pipe(CHILD_RDR, PARENT_WTR); # XXX: check failure?
+ CHILD_WTR->autoflush(1);
+ PARENT_WTR->autoflush(1);
+
+ if ($pid = fork()) {
+ close PARENT_RDR;
+ close PARENT_WTR;
+ print CHILD_WTR "Parent Pid $$ is sending this\n";
+ chomp($line = <CHILD_RDR>);
+ print "Parent Pid $$ just read this: '$line'\n";
+ close CHILD_RDR; close CHILD_WTR;
+ waitpid($pid, 0);
+ } else {
+ die "cannot fork: $!" unless defined $pid;
+ close CHILD_RDR;
+ close CHILD_WTR;
+ chomp($line = <PARENT_RDR>);
+ print "Child Pid $$ just read this: '$line'\n";
+ print PARENT_WTR "Child Pid $$ is sending this\n";
+ close PARENT_RDR;
+ close PARENT_WTR;
+ exit(0);
+ }
But you don't actually have to make two pipe calls. If you
have the socketpair() system call, it will do this all for you.
- #!/usr/bin/perl -w
- # pipe2 - bidirectional communication using socketpair
- # "the best ones always go both ways"
-
- use Socket;
- use IO::Handle; # thousands of lines just for autoflush :-(
-
- # We say AF_UNIX because although *_LOCAL is the
- # POSIX 1003.1g form of the constant, many machines
- # still don't have it.
- socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
- || die "socketpair: $!";
-
- CHILD->autoflush(1);
- PARENT->autoflush(1);
-
- if ($pid = fork()) {
- close PARENT;
- print CHILD "Parent Pid $$ is sending this\n";
- chomp($line = <CHILD>);
- print "Parent Pid $$ just read this: '$line'\n";
- close CHILD;
- waitpid($pid, 0);
- } else {
- die "cannot fork: $!" unless defined $pid;
- close CHILD;
-
chomp($line = <PARENT>);
- print "Child Pid $$ just read this: '$line'\n";
- print PARENT "Child Pid $$ is sending this\n";
- close PARENT;
- exit(0);
- }
+ #!/usr/bin/perl -w
+ # pipe2 - bidirectional communication using socketpair
+ # "the best ones always go both ways"
+
+ use Socket;
+ use IO::Handle; # thousands of lines just for autoflush :-(
+
+ # We say AF_UNIX because although *_LOCAL is the
+ # POSIX 1003.1g form of the constant, many machines
+ # still don't have it.
+ socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
+ || die "socketpair: $!";
+
+ CHILD->autoflush(1);
+ PARENT->autoflush(1);
+
+ if ($pid = fork()) {
+ close PARENT;
+ print CHILD "Parent Pid $$ is sending this\n";
+ chomp($line = <CHILD>);
+ print "Parent Pid $$ just read this: '$line'\n";
+ close CHILD;
+ waitpid($pid, 0);
+ } else {
+ die "cannot fork: $!" unless defined $pid;
+ close CHILD;
+ chomp($line = <PARENT>);
+ print "Child Pid $$ just read this: '$line'\n";
+ print PARENT "Child Pid $$ is sending this\n";
+ close PARENT;
+ exit(0);
+ }
=head1 Sockets: Client/Server Communication
One of the major problems with ancient, antemillennial socket code in Perl
was that it used hard-coded values for some of the constants, which
severely hurt portability. If you ever see code that does anything like
-explicitly setting C<$AF_INET = 2>, you know you're in for big trouble.
+explicitly setting C<$AF_INET = 2>, you know you're in for big trouble.
An immeasurably superior approach is to use the C<Socket> module, which more
reliably grants access to the various constants and functions you'll need.
conformant (be strict in what you provide), but they also recommend
accepting a lone "\012" on input (be lenient in what you require).
We haven't always been very good about that in the code in this manpage,
-but unless you're on a Mac from way back in its pre-Unix dark ages, you'll
+but unless you're on a Mac from way back in its pre-Unix dark ages, you'll
probably be ok.
=head2 Internet TCP Clients and Servers
on a particular interface (like the external side of a gateway
or firewall machine), fill this in with your real address instead.
- #!/usr/bin/perl -Tw
- use strict;
- BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
- use Socket;
- use Carp;
- my $EOL = "\015\012";
+ #!/usr/bin/perl -Tw
+ use strict;
+ BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
+ use Socket;
+ use Carp;
+ my $EOL = "\015\012";
- sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
-
- my $port = shift || 2345;
- die "invalid port" unless if $port =~ /^ \d+ $/x;
+ sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
- my $proto = getprotobyname("tcp");
+ my $port = shift || 2345;
+ die "invalid port" unless $port =~ /^ \d+ $/x;
- socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
- setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
- || die "setsockopt: $!";
- bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
- listen(Server, SOMAXCONN) || die "listen: $!";
+ my $proto = getprotobyname("tcp");
- logmsg "server started on port $port";
+ socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
+ setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
+ || die "setsockopt: $!";
+ bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
+ listen(Server, SOMAXCONN) || die "listen: $!";
- my $paddr;
+ logmsg "server started on port $port";
- $SIG{CHLD} = \&REAPER;
+ my $paddr;
- for ( ; $paddr = accept(Client, Server); close Client) {
- my($port, $iaddr) = sockaddr_in($paddr);
- my $name = gethostbyaddr($iaddr, AF_INET);
+ for ( ; $paddr = accept(Client, Server); close Client) {
+ my($port, $iaddr) = sockaddr_in($paddr);
+ my $name = gethostbyaddr($iaddr, AF_INET);
- logmsg "connection from $name [",
- inet_ntoa($iaddr), "]
- at port $port";
+ logmsg "connection from $name [",
+ inet_ntoa($iaddr), "]
+ at port $port";
- print Client "Hello there, $name, it's now ",
- scalar localtime(), $EOL;
- }
+ print Client "Hello there, $name, it's now ",
+ scalar localtime(), $EOL;
+ }
And here's a multitasking version. It's multitasked in that
like most typical servers, it spawns (fork()s) a slave server to
handle the client request so that the master server can quickly
go back to service a new client.
- #!/usr/bin/perl -Tw
- use strict;
- BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
- use Socket;
- use Carp;
- my $EOL = "\015\012";
+ #!/usr/bin/perl -Tw
+ use strict;
+ BEGIN { $ENV{PATH} = "/usr/bin:/bin" }
+ use Socket;
+ use Carp;
+ my $EOL = "\015\012";
- sub spawn; # forward declaration
- sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
-
- my $port = shift || 2345;
- die "invalid port" unless if $port =~ /^ \d+ $/x;
+ sub spawn; # forward declaration
+ sub logmsg { print "$0 $$: @_ at ", scalar localtime(), "\n" }
- my $proto = getprotobyname("tcp");
+ my $port = shift || 2345;
+ die "invalid port" unless $port =~ /^ \d+ $/x;
- socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
- setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
- || die "setsockopt: $!";
- bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
- listen(Server, SOMAXCONN) || die "listen: $!";
+ my $proto = getprotobyname("tcp");
- logmsg "server started on port $port";
+ socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
+ setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
+ || die "setsockopt: $!";
+ bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
+ listen(Server, SOMAXCONN) || die "listen: $!";
- my $waitedpid = 0;
- my $paddr;
+ logmsg "server started on port $port";
- use POSIX ":sys_wait_h";
- use Errno;
+ my $waitedpid = 0;
+ my $paddr;
- sub REAPER {
- local $!; # don't let waitpid() overwrite current error
- while ((my $pid = waitpid(-1, WNOHANG)) > 0 && WIFEXITED($?)) {
- logmsg "reaped $waitedpid" . ($? ? " with exit $?" : "");
- }
- $SIG{CHLD} = \&REAPER; # loathe SysV
- }
-
- $SIG{CHLD} = \&REAPER;
+ use POSIX ":sys_wait_h";
+ use Errno;
- while (1) {
- $paddr = accept(Client, Server) || do {
- # try again if accept() returned because got a signal
- next if $!{EINTR};
- die "accept: $!";
- };
- my ($port, $iaddr) = sockaddr_in($paddr);
- my $name = gethostbyaddr($iaddr, AF_INET);
-
- logmsg "connection from $name [",
- inet_ntoa($iaddr),
- "] at port $port";
+ sub REAPER {
+ local $!; # don't let waitpid() overwrite current error
+ while ((my $pid = waitpid(-1, WNOHANG)) > 0 && WIFEXITED($?)) {
+ logmsg "reaped $waitedpid" . ($? ? " with exit $?" : "");
+ }
+ $SIG{CHLD} = \&REAPER; # loathe SysV
+ }
- spawn sub {
- $| = 1;
- print "Hello there, $name, it's now ", scalar localtime(), $EOL;
- exec "/usr/games/fortune" # XXX: "wrong" line terminators
- or confess "can't exec fortune: $!";
- };
- close Client;
- }
+ $SIG{CHLD} = \&REAPER;
+
+ while (1) {
+ $paddr = accept(Client, Server) || do {
+ # try again if accept() returned because got a signal
+ next if $!{EINTR};
+ die "accept: $!";
+ };
+ my ($port, $iaddr) = sockaddr_in($paddr);
+ my $name = gethostbyaddr($iaddr, AF_INET);
+
+ logmsg "connection from $name [",
+ inet_ntoa($iaddr),
+ "] at port $port";
+
+ spawn sub {
+ $| = 1;
+ print "Hello there, $name, it's now ",
+ scalar localtime(),
+ $EOL;
+ exec "/usr/games/fortune" # XXX: "wrong" line terminators
+ or confess "can't exec fortune: $!";
+ };
+ close Client;
+ }
- sub spawn {
- my $coderef = shift;
+ sub spawn {
+ my $coderef = shift;
- unless (@_ == 0 && $coderef && ref($coderef) eq "CODE") {
- confess "usage: spawn CODEREF";
- }
+ unless (@_ == 0 && $coderef && ref($coderef) eq "CODE") {
+ confess "usage: spawn CODEREF";
+ }
- my $pid;
- unless (defined($pid = fork())) {
- logmsg "cannot fork: $!";
- return;
- }
- elsif ($pid) {
- logmsg "begat $pid";
- return; # I'm the parent
- }
- # else I'm the child -- go spawn
+ my $pid;
+ unless (defined($pid = fork())) {
+ logmsg "cannot fork: $!";
+ return;
+ }
+ elsif ($pid) {
+ logmsg "begat $pid";
+ return; # I'm the parent
+ }
+ # else I'm the child -- go spawn
- open(STDIN, "<&Client") || die "can't dup client to stdin";
- open(STDOUT, ">&Client") || die "can't dup client to stdout";
- ## open(STDERR, ">&STDOUT") || die "can't dup stdout to stderr";
- exit($coderef->());
- }
+ open(STDIN, "<&Client") || die "can't dup client to stdin";
+ open(STDOUT, ">&Client") || die "can't dup client to stdout";
+ ## open(STDERR, ">&STDOUT") || die "can't dup stdout to stderr";
+ exit($coderef->());
+ }
This server takes the trouble to clone off a child version via fork()
for each incoming request. That way it can handle many requests at
L</Deferred Signals (Safe Signals)> above) in Perl 5.8.0 means that
accept() might also be interrupted when the process receives a signal.
This typically happens when one of the forked subprocesses exits and
-notifies the parent process with a CHLD signal.
+notifies the parent process with a CHLD signal.
If accept() is interrupted by a signal, $! will be set to EINTR.
If this happens, we can safely continue to the next iteration of
the loop and another call to accept(). It is important that your
-signal handling code not modify the value of $!, or else this test
+signal handling code not modify the value of $!, or else this test
will likely fail. In the REAPER subroutine we create a local version
of $! before calling waitpid(). When waitpid() sets $! to ECHILD as
-it inevitably does when it has no more children waiting, it
+it inevitably does when it has no more children waiting, it
updates the local copy and leaves the original unchanged.
You should use the B<-T> flag to enable taint checking (see L<perlsec>)
printf "%-24s ", $host;
my $hisiaddr = inet_aton($host) || die "unknown host";
my $hispaddr = sockaddr_in($port, $hisiaddr);
- socket(SOCKET, PF_INET, SOCK_STREAM, $proto)
+ socket(SOCKET, PF_INET, SOCK_STREAM, $proto)
|| die "socket: $!";
connect(SOCKET, $hispaddr) || die "connect: $!";
my $rtime = pack("C4", ());
unless (defined($pid = fork())) {
logmsg "cannot fork: $!";
return;
- }
+ }
elsif ($pid) {
logmsg "begat $pid";
return; # I'm the parent
- }
+ }
else {
# I'm the child -- go spawn
}
PeerAddr => "localhost",
PeerPort => "daytime(13)",
)
- || die "can't connect to daytime service on localhost";
+ || die "can't connect to daytime service on localhost";
while (<$remote>) { print }
When you run this program, you should get something back that
$client->autoflush(1);
print $client "Welcome to $0; type help for command list.\n";
$hostinfo = gethostbyaddr($client->peeraddr);
- printf "[Connect from %s]\n", $hostinfo ? $hostinfo->name : $client->peerhost;
+ printf "[Connect from %s]\n",
+ $hostinfo ? $hostinfo->name : $client->peerhost;
print $client "Command? ";
while ( <$client>) {
- next unless /\S/; # blank line
- if (/quit|exit/i) { last }
- elsif (/date|time/i) { printf $client "%s\n", scalar localtime() }
- elsif (/who/i ) { print $client `who 2>&1` }
- elsif (/cookie/i ) { print $client `/usr/games/fortune 2>&1` }
- elsif (/motd/i ) { print $client `cat /etc/motd 2>&1` }
+ next unless /\S/; # blank line
+ if (/quit|exit/i) { last }
+ elsif (/date|time/i) { printf $client "%s\n", scalar localtime() }
+ elsif (/who/i ) { print $client `who 2>&1` }
+ elsif (/cookie/i ) { print $client `/usr/games/fortune 2>&1` }
+ elsif (/motd/i ) { print $client `cat /etc/motd 2>&1` }
else {
print $client "Commands: quit date who cookie motd\n";
}
using select() to do a timed-out wait for I/O. To do something similar
with TCP, you'd have to use a different socket handle for each host.
- #!/usr/bin/perl -w
- use strict;
- use Socket;
- use Sys::Hostname;
-
- my ( $count, $hisiaddr, $hispaddr, $histime,
- $host, $iaddr, $paddr, $port, $proto,
- $rin, $rout, $rtime, $SECS_OF_70_YEARS);
-
- $SECS_OF_70_YEARS = 2_208_988_800;
-
- $iaddr = gethostbyname(hostname());
- $proto = getprotobyname("udp");
- $port = getservbyname("time", "udp");
- $paddr = sockaddr_in(0, $iaddr); # 0 means let kernel pick
-
- socket(SOCKET, PF_INET, SOCK_DGRAM, $proto) || die "socket: $!";
- bind(SOCKET, $paddr) || die "bind: $!";
-
- $| = 1;
- printf "%-12s %8s %s\n", "localhost", 0, scalar localtime();
- $count = 0;
- for $host (@ARGV) {
- $count++;
- $hisiaddr = inet_aton($host) || die "unknown host";
- $hispaddr = sockaddr_in($port, $hisiaddr);
- defined(send(SOCKET, 0, 0, $hispaddr)) || die "send $host: $!";
- }
+ #!/usr/bin/perl -w
+ use strict;
+ use Socket;
+ use Sys::Hostname;
+
+ my ( $count, $hisiaddr, $hispaddr, $histime,
+ $host, $iaddr, $paddr, $port, $proto,
+ $rin, $rout, $rtime, $SECS_OF_70_YEARS);
+
+ $SECS_OF_70_YEARS = 2_208_988_800;
+
+ $iaddr = gethostbyname(hostname());
+ $proto = getprotobyname("udp");
+ $port = getservbyname("time", "udp");
+ $paddr = sockaddr_in(0, $iaddr); # 0 means let kernel pick
+
+ socket(SOCKET, PF_INET, SOCK_DGRAM, $proto) || die "socket: $!";
+ bind(SOCKET, $paddr) || die "bind: $!";
+
+ $| = 1;
+ printf "%-12s %8s %s\n", "localhost", 0, scalar localtime();
+ $count = 0;
+ for $host (@ARGV) {
+ $count++;
+ $hisiaddr = inet_aton($host) || die "unknown host";
+ $hispaddr = sockaddr_in($port, $hisiaddr);
+ defined(send(SOCKET, 0, 0, $hispaddr)) || die "send $host: $!";
+ }
- $rin = "";
- vec($rin, fileno(SOCKET), 1) = 1;
-
- # timeout after 10.0 seconds
- while ($count && select($rout = $rin, undef, undef, 10.0)) {
- $rtime = "";
- $hispaddr = recv(SOCKET, $rtime, 4, 0) || die "recv: $!";
- ($port, $hisiaddr) = sockaddr_in($hispaddr);
- $host = gethostbyaddr($hisiaddr, AF_INET);
- $histime = unpack("N", $rtime) - $SECS_OF_70_YEARS;
- printf "%-12s ", $host;
- printf "%8d %s\n", $histime - time(), scalar localtime($histime);
- $count--;
- }
+ $rin = "";
+ vec($rin, fileno(SOCKET), 1) = 1;
+
+ # timeout after 10.0 seconds
+ while ($count && select($rout = $rin, undef, undef, 10.0)) {
+ $rtime = "";
+ $hispaddr = recv(SOCKET, $rtime, 4, 0) || die "recv: $!";
+ ($port, $hisiaddr) = sockaddr_in($hispaddr);
+ $host = gethostbyaddr($hisiaddr, AF_INET);
+ $histime = unpack("N", $rtime) - $SECS_OF_70_YEARS;
+ printf "%-12s ", $host;
+ printf "%8d %s\n", $histime - time(), scalar localtime($histime);
+ $count--;
+ }
This example does not include any retries and may consequently fail to
contact a reachable host. The most prominent reason for this is congestion
manpage describes the low-level interface to sockets. Besides the obvious
functions in L<perlfunc>, you should also check out the F<modules> file at
your nearest CPAN site, especially
-L<http://www.cpan.org/modules/00modlist.long.html#ID5_Networking_>.
+L<http://www.cpan.org/modules/00modlist.long.html#ID5_Networking_>.
See L<perlmodlib> or best yet, the F<Perl FAQ> for a description
-of what CPAN is and where to get it if the previous link doesn't work
+of what CPAN is and where to get it if the previous link doesn't work
for you.
Section 5 of CPAN's F<modules> file is devoted to "Networking, Device
https://perl5.git.perl.org / perl5.git / blobdiff