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Broc Seib


Tie::Syslog - Tie a filehandle to Syslog. If you Tie STDERR, then all STDERR errors are automatically caught, or you can debug by Carp'ing to STDERR, etc. (Good for CGI error logging.)


  use Tie::Syslog;

  ##  Pass up to four args:
  ##    facility.priority   ('local0.error')  ## note Linux uses 'err'
  ##    identity            ('my_program')
  ##    log options         ('pid')
  ##    setlogsock          ('inet'|'unix')
  tie *MYLOG, 'Tie::Syslog','local0.error','my_program','pid','inet';

  print MYLOG "I made an error."; ## this will be syslogged
  printf MYLOG "Error %d", 42;    ## syslog as "Error 42"

  untie *MYLOG;

  ##  Special case: pass a ref to file glob as first arg.
  ##  This stores the filehandle and uses it to implement calls
  ##  like fileno() and binmode() etc...
  tie *STDERR, \*STDERR, 'Tie::Syslog','local0.error','my_app','pid','inet';

  ##  yeah, it looks funny, but is the only way...?


This module allows you to tie a filehandle (output only) to syslog. This becomes useful in general when you want to capture any activity that happens on STDERR and see that it is syslogged for later perusal. You can also create an arbitrary filehandle, say LOG, and send stuff to syslog by printing to this filehandle. This module depends on the Sys::Syslog module to actually get info to syslog.

Tie your filehandle to syslog using a glob to the filehandle. When it is tied to the 'Tie::Syslog' class, you may optionally pass four arguments that determine the behavior of the output bound to syslog.

You first specify a facility and priority to direct your filehandle traffic to the proper channels in syslog. I suggest reviewing a manpage for syslog on your local system to identify what the facilities and priorities actually are. Nonetheless, this first argument is specified as a string consisting of the facility followed by a dot, followed by the priority. For example, the default setting is 'local0.error'. (Note: I believe Linux uses 'err' rather than 'error'.) If you do not specify a first arg, this default is used.

The second argument is an identifier string. This is the string that shows up in evey line of output that syslog writes. You may use this identifier to help sort out syslog lines produced by different applications (with different id's.) If you do not specify a value for this argument, it will default to the name of the running program. (This is derived from the special $0 variable, stripping off everything up to the final appearing forward slash character.)

The third argument is a string of comma separated log options specific to syslog. Current documentation supports 'pid,cons,ndelay,nowait'. Check your local listings, as you may pass values that are only part of your local system. I suggest checking your man pages for syslog, and perhaps looking inside your site_perl/$archname/sys/syslog.ph for other such values. If you do not pass this third argument, it defaults to the string 'pid', which makes syslog put a [12345] pid value on each line of output.

The fourth argument is either the string 'inet' or 'unix'. This is passed to the Sys::Syslog::setlogsock() call to specify the socket type to be used when opening the connection to syslog. If this argument is not specified, then the default used is 'inet'. Many perl installations still have original Sys::Syslog which does not have the setlogsock() routine. There is also no $VERSION constant to test in Sys::Syslog, so we'll test the symbol table to see if the routine exists. If the routine does not exist, then the fourth argument is silently ignored. I did not want to require people to have "the latest" version of perl just to use this module.

Note: You can now optionally pass a reference to a Filehandle as the *very* first arg (before the 'Tie::Syslog' even...) The *only* time you'd do this is if you are experiencing trouble using your tied filehandle with other code that expects to do calls like fileno() and binmode() to operate on this tied filehandle. The TIEHANDLE api gives us no way (that I have found) to get access to the actual tied variable, or filehandle in this case. So, I have resorted to just passing it in as a arg right up front and just storing it in the object. **THERE ARE PROBLEMS WITH THIS!!!** Be aware, those of you this may affect...

An aside on using 'STDERR':

The blessed object that is returned from tie also has one additional member function. In the case that you tie the filehandle 'STDERR' (or a dup'ed copy of STDERR) then you may want to capture information going to the warn() and die() functions. You may call ExtendedSTDERR() to setup the proper handler function to deal with the special signals for __DIE__ and __WARN__. Because this module really has no knowledge of what filehandle is being tied, I contemplated trying to make this automatic for when the STDERR filehandle is used. But, alas, one may have a different name for what is really STDERR, plus the TIEHANDLE function has no way of knowing what the filehandle symbol is anyway. I also decided to put the logic of how to handle the two signal cases into this module, when perhaps they might be more suited to be at the level of whoever is calling this module. Well, you don't have to call the routine ExtendedSTDERR() if you don't like what it does. I felt obligated to provide a proper solution to the signal handling since a common use of this module would be to capture STDERR for syslogging.

  my $x = tie *STDERR, 'Tie::Syslog', 'local0.debug';
  $x->ExtendedSTDERR();            ## set __DIE__,__WARN__ handler

  print STDERR "I made an error."; ## this will be syslogged
  printf STDERR "Error %d", 42;    ## syslog as "Error 42"
  warn "Another error was made.";  ## this will also be syslogged
  eval {
      die "exception thrown";      ## this is *NOT* syslogged
  die "Killing me softly?!";       ## syslogged, then script ends

  undef $x;                        ## be sure to do this, else warns!
  untie *STDERR;

When used with STDERR, combined with the good habit of using the perl -w switch, this module happens to be useful in catching unexpected errors in any of your code, or team's code. Tie::Syslog is pretty brain-dead. However, it can become quite flexible if you investigate your options with the actual syslog daemon. Syslog has a variety of options available, including notifying console, logging to other machines running syslog, or email support in the event of Bad Things. Consult your syslog documentation to get /etc/syslog.conf setup by your sysadmin and use Tie::Syslog to get information into those channels.


If you do not specify an identity (2nd arg) to tie() it defaults to the name of the executable via special var $0. It is split by the character '/', so non-unix systems will end up with a "full name" for its identity, if left unspecified. I could use File::Spec for non-unix paths -- but how many of you non-unix persons out there have syslog and would like this? Tell me...


Copyright (c) 1999-2002 Broc Seib. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


$Id: Syslog.pm,v 1.8 2002/01/21 03:24:12 bseib Exp $


Read perldoc perltie for info on how to tie a filehandle. Read perldoc Sys::Syslog. Read man syslog to learn more about syslog.