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Chapter 16 Process Management and Communication |
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The following
program gives you random signatures by using named pipes. It expects the signatures file to have records in the format of the
fortune
program - that is, each possible multiline record is terminated with
"%%\n"
. Here's an example:
Make is like Pascal: everybody likes it, so they go in and change it. --Dennis Ritchie %% I eschew embedded capital letters in names; to my prose-oriented eyes, they are too awkward to read comfortably. They jangle like bad typography. --Rob Pike %% God made the integers; all else is the work of Man. --Kronecker %% I'd rather have :rofix than const. --Dennis Ritchie %% If you want to program in C, program in C. It's a nice language. I use it occasionally... :-) --Larry Wall %% Twisted cleverness is my only skill as a programmer. --Elizabeth Zwicky %% Basically, avoid comments. If your code needs a comment to be understood, it would be better to rewrite it so it's easier to understand. --Rob Pike %% Comments on data are usually much more helpful than on algorithms. --Rob Pike %% Programs that write programs are the happiest programs in the world. --Andrew Hume %%
We check whether we're already running by using a file with our PID in it. If sending a signal number 0 indicates that PID still exists (or, rarely, that something else has reused it), we just exit. We also look at the current Usenet posting to decide whether to look for a per-newsgroup signature file. That way, you can have different signatures for each newsgroup you post to. For variety, a global signature file is still on occasion used even if a per-newsgroup file exists.
You can even use
sigrand
on systems without named pipes if you remove the code to create a named pipe and extend the sleep interval before file updates. Then
.signature
would just be a regular file. Another portability concern is that the program forks itself in the background, which is almost like becoming a
daemon. If you have no
fork
call, just comment it out.
The full program is shown in Example 16.12 .
#!/usr/bin/perl -w # sigrand - supply random fortunes for .signature file use strict; # config section variables use vars qw( $NG_IS_DIR $MKNOD $FULLNAME $FIFO $ART $NEWS $SIGS $SEMA $GLOBRAND $NAME ); # globals use vars qw( $Home $Fortune_Path @Pwd ); ################################################################ # begin configuration section # should really read from ~/.sigrandrc gethome(); # for rec/humor/funny instead of rec.humor.funny $NG_IS_DIR = 1; $MKNOD = "/bin/mknod"; $FULLNAME = "$Home/.fullname"; $FIFO = "$Home/.signature"; $ART = "$Home/.article"; $NEWS = "$Home/News"; $SIGS = "$NEWS/SIGNATURES"; $SEMA = "$Home/.sigrandpid"; $GLOBRAND = 1/4; # chance to use global sigs anyway # $NAME should be (1) left undef to have program guess # read address for signature maybe looking in ~/.fullname, # (2) set to an exact address, or (3) set to empty string # to be omitted entirely. $NAME = ''; # means no name used ## $NAME = "me\@home.org\n"; # end configuration section -- HOME and FORTUNE get autoconf'd ################################################################ setup(); # pull in inits justme(); # make sure program not already running fork && exit; # background ourself and go away open (SEMA, "> $SEMA") or die "can't write $SEMA: $!"; print SEMA "$$\n"; close(SEMA) or die "can't close $SEMA: $!"; # now loop forever, writing a signature into the # fifo file. if you don't have real fifos, change # sleep time at bottom of loop to like 10 to update # only every 10 seconds. for (;;) { open (FIFO, "> $FIFO") or die "can't write $FIFO: $!"; my $sig = pick_quote(); for ($sig) { s/^((:?[^\n]*\n){4}).*$/$1/s; # trunc to 4 lines s/^(.{1,80}).*? *$/$1/gm; # trunc long lines } # print sig, with name if present, padded to four lines if ($NAME) { print FIFO $NAME, "\n" x (3 - ($sig =~ tr/\n//)), $sig; } else { print FIFO $sig; } close FIFO; # Without a microsleep, the reading process doesn't finish before # the writer tries to open it again, which since the reader exists, # succeeds. They end up with multiple signatures. Sleep a tiny bit # between opens to give readers a chance to finish reading and close # our pipe so we can block when opening it the next time. select(undef, undef, undef, 0.2); # sleep 1/5 second } die "XXX: NOT REACHED"; # you can't get here from anywhere ################################################################ # Ignore SIGPIPE in case someone opens us up and then closes the fifo # without reading it; look in a .fullname file for their login name. # Try to determine the fully qualified hostname. Look our for silly # ampersands in passwd entries. Make sure we have signatures or fortunes. # Build a fifo if we need to. sub setup { $SIG{PIPE} = 'IGNORE'; unless (defined $NAME) { # if $NAME undef in config if (-e $FULLNAME) { $NAME = `cat $FULLNAME`; die "$FULLNAME should contain only 1 line, aborting" if $NAME =~ tr/\n// > 1; } else { my($user, $host); chop($host = `hostname`); ($host) = gethostbyname($host) unless $host =~ /\./; $user = $ENV{USER} || $ENV{LOGNAME} || $Pwd[0] or die "intruder alert"; ($NAME = $Pwd[6]) =~ s/,.*//; $NAME =~ s/&/\u\L$user/g; # can't believe some folks still do this $NAME = "\t$NAME\t$user\@$host\n"; } } check_fortunes() if !-e $SIGS; unless (-p $FIFO) { # -p checks whether it's a named pipe if (!-e _) { system("$MKNOD $FIFO p") && die "can't mknod $FIFO"; warn "created $FIFO as a named pipe\n"; } else { die "$0: won't overwrite file .signature\n"; } } else { warn "$0: using existing named pipe $FIFO\n"; } # get a good random number seed. not needed if 5.004 or better. srand(time() ^ ($$ + ($$ << 15))); } # choose a random signature sub pick_quote { my $sigfile = signame(); if (!-e $sigfile) { return fortune(); } open (SIGS, "< $sigfile" ) or die "can't open $sigfile"; local $/ = "%%\n"; local $_; my $quip; rand($.) < 1 && ($quip = $_) while <SIGS>; close SIGS; chomp $quip; return $quip || "ENOSIG: This signature file is empty.\n"; } # See whether ~/.article contains a Newsgroups line. if so, see the first # group posted to and find out whether it has a dedicated set of fortunes. # otherwise return the global one. also, return the global one randomly # now and then to spice up the sigs. sub signame { (rand(1.0) > ($GLOBRAND) && open ART) || return $SIGS; local $/ = ''; local $_ = <ART>; my($ng) = /Newsgroups:\s*([^,\s]*)/; $ng =~ s!\.!/!g if $NG_IS_DIR; # if rn -/, or SAVEDIR=%p/%c $ng = "$NEWS/$ng/SIGNATURES"; return -f $ng ? $ng : $SIGS; } # Call the fortune program with -s for short flag until # we get a small enough fortune or ask too much. sub fortune { local $_; my $tries = 0; do { $_ = `$Fortune_Path -s`; } until tr/\n// < 5 || $tries++ > 20; s/^/ /mg; $_ || " SIGRAND: deliver random signals to all processes.\n"; } # Make sure there's a fortune program. Search # for its full path and set global to that. sub check_fortunes { return if $Fortune_Path; # already set for my $dir (split(/:/, $ENV{PATH}), '/usr/games') { return if -x ($Fortune_Path = "$dir/fortune"); } die "Need either $SIGS or a fortune program, bailing out"; } # figure out our directory sub gethome { @Pwd = getpwuid($<); $Home = $ENV{HOME} || $ENV{LOGDIR} || $Pwd[7] or die "no home directory for user $<"; } # "There can be only one." --the Highlander sub justme { if (open SEMA) { my $pid; chop($pid = <SEMA>); kill(0, $pid) and die "$0 already running (pid $pid), bailing out"; close SEMA; }
}
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| 16.21. Timing Out an Operation |
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17. Sockets |
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