Dear Monks,

I fear this may well be a FAQ or the combination of a couple of them. Forgive me if this is the case.

All I want is to lock a file. Truthfully. Its got so bad that this is the limit of my ambition. In the main I'm not a perl numpty, but this is driving my looney.

Running on an FC4 box I have the following code to reset (i.e. remove) an entry from the current user's ssh known_hosts file. I cannot get the lock to work. I have commented some of the artifacts of what I've already tried. Please guide me to enlightenment. 

#!/usr/bin/perl

my $host = $ARGV[0];
my $known_hosts = './kh.tt';

##USE '>>' OTHERWISE WE WILL TRUNCATE AT open() - BEFORE WE HAVE THE L
+OCK!!
#do{
#   print 'Error opening ssh known hosts file : ', $!, "\n";
#   exit;
#}unless( open KNOWN_HOSTS, ">> $known_hosts" );

open LOCK, "> $known_hosts.sem" or die "Can't open semaphore: $!\n";

##lock the file
my $lock_tries = 3;
my $got_lock = 0;
GETLOCK: while( $lock_tries )
{
   print "TRYING FOR LOCK ($lock_tries)\n";
   #if( flock(KNOWN_HOSTS, LOCK_EX|LOCK_NB) )
   my $ret = flock(LOCK, LOCK_EX|LOCK_NB);
   print "Flock ret : $ret\n";
   if( $ret )
   {
      print "GOT LOCK\n";
      $got_lock = 1;
      last GETLOCK;
   }
   sleep(1);
   $lock_tries --;
}

do{
   print 'Unable to lock known hosts file for updates', "\n";
   close LOCK;
   exit;
} unless($got_lock == 1);


#open KNOWN_HOSTS_RD, "< $known_hosts";
open KNOWN_HOSTS, "+< $known_hosts" or die "Can't open data file: $!\n
+";
#my @host_data = <KNOWN_HOSTS_RD>;
my @host_data = <KNOWN_HOSTS>;
#close KNOWN_HOSTS_RD;
my $host_pattern = $host;
$host_pattern =~ s/\./\\\./;
my @new_data = grep(!/^$host_pattern/,@host_data);
truncate KNOWN_HOSTS, 0;
print KNOWN_HOSTS join("\n", @new_data);

##This releases the lock.
close(KNOWN_HOSTS);

close LOCK;

[download]
Many thanks for any help.

In reply to flock(), dodgy return? by danstuken

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