06-19-2008
piping and backgroud processes (daemons)
Hello to all,
I've a strage problem here:
a perl script that parses the output of sar -q 300 0 (one line of performace data each 5 min. infinately) works fine from the CLI. It processes one line output every 5 minutes.
If i disconnect it from the terminal (executing it with cron, nohup startporc etc...) no output is processed until sar has completed (using sar -q 1 20).
then all 20 llines output are processed at the same time.
Code
Quote:
open (SAR,"/usr/bin/sar -q 1 4&|") or die "Cant open sar" ;
while (<SAR>){
chomp;
# write the output into a rrd database
}
close (SAR);
the script is supposed to run as "demon" in the backdround to ubdate
performance reports every 5 minutes, so i need to process the output just in time.
As far as i foun out it is not a Perl problem rather than the way linux handels pipes on processes not running on a terminal.
any ideas ?
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PPERL(1p) User Contributed Perl Documentation PPERL(1p)
NAME
PPerl - Make perl scripts persistent in memory
SYNOPSIS
$ pperl foo.pl
DESCRIPTION
This program turns ordinary perl scripts into long running daemons, making subsequent executions extremely fast. It forks several processes
for each script, allowing many processes to call the script at once.
It works a lot like SpeedyCGI, but is written a little differently. I didn't use the SpeedyCGI codebase, because I couldn't get it to
compile, and needed something ASAP.
The easiest way to use this is to change your shebang line from:
#!/usr/bin/perl -w
To use pperl instead:
#!/usr/bin/pperl -w
WARNINGS
Like other persistent environments, this one has problems with things like BEGIN blocks, global variables, etc. So beware, and try checking
the mod_perl guide at http://perl.apache.org/guide/ for lots of information that applies to many persistent perl environments.
Parameters
$ pperl <perl params> -- <pperl params> scriptname <script params>
The perl params are sent to the perl binary the first time it is started up. See perlrun for details.
The pperl params control how pperl works. Try -h for an overview.
The script params are passed to the script on every invocation. The script also gets any current environment variables, the current working
directory, and everything on STDIN.
Killing
In order to kill a currently running PPerl process, use:
pperl -- -k <scriptname>
You need to make sure the path to the script is the same as when it was invoked.
Alternatively look for a .pid file for the script in your tmp directory, and kill (with SIGINT) the process with that PID.
ENVIRONMENT
pperl uses the PPERL_TMP_PATH environment variable to determine the directory where to store the files used for inter-process
communication. By default, the subdirectory .pperl of the user's home directory is used.
BUGS
The process does not reload when the script or modules change.
$^S is not represented identically with respect to perl, since your script will be run within an eval block
AUTHOR
Matt Sergeant, matt@sergeant.org. Copyright 2001 MessageLabs Ltd.
SEE ALSO
perl. perlrun.
perl v5.14.2 2011-11-15 PPERL(1p)