Article 8659 of comp.lang.perl:
Xref: feenix.metronet.com alt.sources:2388 comp.lang.perl:8659 news.software.b:2867
Newsgroups: alt.sources,comp.lang.perl,news.software.b
Path: feenix.metronet.com!news.ecn.bgu.edu!usenet.ins.cwru.edu!gatech!swrinde!sgiblab!a2i!dhesi
From: [email protected] (Rahul Dhesi)
Subject: update 'min' and 'max' fields in 'active' file
Message-ID: <[email protected]>
Followup-To: alt.sources.d,comp.lang.perl,news.software.b
Sender: [email protected] (Usenet News)
Nntp-Posting-Host: bolero
Organization: a2i network
Date: Mon, 6 Dec 1993 09:21:14 GMT
Lines: 254

Checksum:  204823036 (verify with 'brik')
Submitter: Rahul Dhesi <[email protected]>
Archive-name: perl-source/dhesi/updminmax

#! /usr/bin/perl

# (C) Copyright 1993 Rahul Dhesi, All rights reserved.
# Permission for copying and creation of derivative works is granted,
# provided this copyright notice is preserved, to anybody who
# does not discriminate against the copyright owner.

# $Source: /news/bin/RCS/updminmax,v $
# $Id: updminmax,v 1.17 1993/12/06 09:12:31 news Exp $
#
# Update min and max fields in active file.  Based on ideas in
# two shell scripts that come with C-News.  This program
# gets newsgroup names from the active file, gets the article numbers
# from the spool directory for each newsgroup, and corrects the min
# and max fields in the active file.  It is useful for keeping the
# min field updated.  It is also useful for correcting errors in the
# max field, which have been known to occur occasionally.  A field length
# of 5 digits for the min field and 10 digits for the max field
# is forced -- this can be changed in the code by revising two
# sprintf statements.  The entire news system is locked while this program
# runs.  At the a2i network this program completes in about 8 to 10
# minutes.  Locking is done by creating a symbolic link.
#
# This script is offered "as is", though it appears to work under
# SunOS 4.1.1 running C-News derived from the May 1992 release and
# using perl 4.019.

$myname = "updminmax";

# Configuration information
$NEWSCTL = '/news/lib';         # news lib (where active file resides)
$NEWSARTS = '/news/news';       # news spool (where articles reside)

# following will be changed only rarely
$ACTIVE = 'active';                     # name of active file
$BACKUP = "$ACTIVE.before.$myname";     # back up active file by this name
$INF = (1 << 30);               # large no. bigger than all article numbers
$ona2i = 0;                     # are we on the a2i network?

$RCSHEADER = '$Source: /news/bin/RCS/updminmax,v $' . "\n" .
       '$Id: updminmax,v 1.17 1993/12/06 09:12:31 news Exp $';

$usage = "usage: $myname [-vtxnmCD] arg ... (or -h for help)";

if ($ARGV[0] =~ "^-.+" ) {
  require "getopts.pl";
  &Getopts("vtxhnmCD");
}

$debug = $opt_x;
$trace = $opt_t;
$verbose = $debug || $trace || $opt_v;

$nolock = $opt_n;
$clean = $opt_C;
$diff = $opt_D;
$summarize_max = $opt_m;

if ($opt_h) {
  &givehelp();
  exit(0);
}

chdir($NEWSCTL) || die "$myname: error: can't cd to $NEWSCTL: $!\n";
open(ACTIVE, $ACTIVE) ||
  die "$myname: error: can't read $ACTIVE file: $!\n";

if (! $trace) {
  $newactive = "$ACTIVE.new.$$"; unlink($newactive);
  (-f $newactive) && die "$myname: error: can't unlink $newactive\n";
  open(NEWACTIVE, ">$newactive") ||
     die "$myname: error: can't write to $newactive\n";
}

if ($verbose) {
  $| = 1;
}

# trap signals so we can unlock any lock on a signal
$SIG{'INT'} = 'signal';
$SIG{'TERM'} = 'signal';
$SIG{'QUIT'} = 'signal';
$SIG{'TERM'} = 'signal';
$SIG{'PIPE'} = 'signal';
# lock news system -- will wait forever for lock
&newslock() unless $nolock;

$trace && print "$myname: TRACE: no writes to disk\n";

# do it
eval '&main';
&newsunlock unless $nolock;
$@ && die $@;
exit;

sub main {
  while (<ACTIVE>) {
     ($group, $max, $min, $fourth) = split(' ', $_);
     (! $fourth) && die "$myname: fatal: less than 4 fields in $ACTIVE\n";
     ($dir = $group) =~ s#\.#/#g;              # map ng name to directory name
     if (opendir(DIR, "$NEWSARTS/$dir")) {
        $newmax = 0;
        $newmin = $INF;                        # infinity

        # find min and max fields by reading  directory entries
        while ($entry = readdir(DIR)) {
           if ($entry =~ /^\d+$/) {    # if all numeric
              if ($entry < $newmin) {
                 $newmin = $entry;
              }
              if ($entry > $newmax) {
                 $newmax = $entry;
              }
           } elsif ($debug) {
              if ($entry ne '.' && $entry ne '..' && $entry ne '.overview') {
                 print "non-numeric: $NEWSARTS/$dir/$entry\n";
              }
           }
        }
        if ($newmin == $INF) {
           # no articles found
           $newmax = $max;             # old value of max
           $newmin = $max + 1;         # .. and min is one higher
        }
        # don't let max get smaller.
        if ($newmax < $max) {
           $newmax = $max;
        }
        $newmin = sprintf("%05u", $newmin);
        $newmax = sprintf("%010u", $newmax);
        print NEWACTIVE "$group $newmax $newmin $fourth\n";
        $verbose && print "$group $newmax $newmin $fourth\n";
        if ($summarize_max && $max != $newmax) {
           printf "ng %20s max $max -> $newmax, min $min -> $newmin\n",
              $group;
        }
     } else {
        if ($clean) {
           $verbose && "$myname: omitting $group: no spool directory\n";
        } else {
           print NEWACTIVE "$group $max $min $fourth\n";
           $verbose && print "$group $max $min $fourth\n";
        }
     }
  }
  close(ACTIVE);
  close(NEWACTIVE);

  if (! $trace) {
     if ($diff) {
        system "diff -u $ACTIVE $newactive > $ACTIVE.diff 2>&1";
     }
     $oldlen = `wc -l < '$ACTIVE'`;  chop $oldlen;
     $newlen = `wc -l < $newactive`; chop $newlen;
     if ($oldlen == $newlen) {
        # a2i use only -- preserve a numbered copy of the active file
        $ona2i && system("/news/bin/jab -P $ACTIVE");
        unlink $BACKUP;
        link($ACTIVE, $BACKUP) ||
           warn "$myname: could not link $ACTIVE to $BACKUP: $!\n";
        rename($newactive, $ACTIVE) ||
           die "$myname: error: rename $newactive $ACTIVE: $!\n";
     } else {
       die "$myname: $newactive is bad; aborting, leaving $ACTIVE unchanged\n";
     }
  }
}

## sub usage_error {
##    local($msg) = @_;
##    if ($msg) {
##       die "$msg\n";
##    } else {
##       die "$usage\n";
##    }
## }

sub givehelp {
  ## require 'local/page.pl';
  ## &page(<<EOF);
  print <<EOF;
$usage

This program updates min and max fields in the $ACTIVE file.  It locks the
entire news system while it runs.

  -C           Clean $ACTIVE file by omitting groups whose spool
               directories could not be accessed.
  -m           When a max field is changed, print min and max changes to
               stdout.
  -D           Save a diff of original and updated active file
               into $ACTIVE.diff.
  -v           Be verbose.
  -t           Trace only -- show what would be done but don't do it.
               The news system will not be locked.
  -x           Enable debugging -- for program maintainers.
  -n           Don't lock news system (risky to use this except for testing)

$RCSHEADER
EOF
}

# Lock the news system putting into the global variable @UNLOCK_LIST
# a list of filenames to be deleted when &newsunlock is called.
sub newslock {
  $lock = "$NEWSCTL/LOCK";
  local($ltemp) = "$NEWSCTL/L.$$";
  @UNLOCK_LIST && die "$myname: newslock: internal error: " .
     "nonempty UNLOCK_LIST: @UNLOCK_LIST\n";

  @UNLOCK_LIST = ($ltemp);             # newsunlock will delete these

  if ($trace) {
     print "newslock: trace: would lock: $lock -> $ltemp\n";
     return;
  }

  open(LTEMP, ">$ltemp") || die "$myname: error: news lock failed\n";
  print LTEMP "$$" || die "$myname: error: news lock failed\n";
  close(LTEMP);

  for ( ; ; ) {
     if (symlink($ltemp, $lock)) {
        push(@UNLOCK_LIST, $lock);
        $debug && print "$myname: debug: locked: $lock -> $ltemp\n";
        return;
     }
     $verbose && print "$myname: debug: waiting 30 seconds for lock\n";
     sleep(30);
  }
}

sub newsunlock {
  if (@UNLOCK_LIST) {
     $verbose && print "newsunlock: unlink @UNLOCK_LIST\n";
     (! $trace) && unlink @UNLOCK_LIST;
  } else {
     $verbose && print "newsunlock: empty UNLOCK_LIST\n";
  }
}

# signal handler
# -- newsunlock, then exit
sub signal {
  &newsunlock();
  unlink $newactive;
  exit;
}

##### == END ==

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