I recently created a perl script (lets call it 1.) to process a network trace and compute the number of bytes received for a given protocol (e.g. udp, tcp or routing protocols such as AODV, DSR) for a given time interval for each node in the trace. The output of this is a comma seperated value (CSV) delimited output to STDOUT, which I redirect into a file when invoked from cmd using the standard > operator, for graphing.
Today I wanted to compute routing protocol overheads, as a percentage of routing packets vs. all packets (data and routing) for a network trace. This requires running perl script (1.) twice with different protocol numbers so I thought writing a container perl script to invoke script (1.) was the way to go. I admit I’m a bit of a perl newbie so please bear with me if this is obvious!
The perl script needed to achieve several objectives:
- Redirect STDOUT to a variable
- Execute perl script (1.) for ALL protocols
- Process variable holding STDOUT into data structure
- Repeat steps 2 and 3 for routing protocol.
- Reset STDOUT.
- Perform calculation from two data structures and output routing overheads as CSV, which I could redirect to a file using standard > operator.
Here’s the code:
my $var;open(OLDOUT,">&STDOUT") or die "Unable to save STDOUT $!\\n"; #save STDOUT handle to OLDOUTclose STDOUT;open(STDOUT,">", \\$var) || die "Unable to open STDOUT: $!"; #open STDOUT handle to use $var@ARGV = ($opt\_infile,$opt\_class,$opt\_ipaddr,"all","table",$opt\_start\_time,$opt\_end\_time);#invoke perl script (1.) with above argsdo("datareceived2.pl");my @dataandroutingcsv = split "\\n",$var;open(STDOUT,">&OLDOUT");#process @dataandroutingcsv removed for brevityclose STDOUT;#reinit $varundef $var;open(STDOUT,">", \\$var) || die "Unable to open STDOUT: $!"; #reopen STDOUT to use $var@ARGV = ($opt\_infile,$opt\_class,$opt\_ipaddr,$opt\_protocol,"table",$opt\_start\_time,$opt\_end\_time);#invoke perl script (1.) again with new argsdo("datareceived2.pl");my @routingcsv = split "\\n",$var;open(STDOUT,">&OLDOUT"); #redirect STDOUT to use OLDOUT (for printing results to console)#process @routingcsv, print result CSV removed for brevity
Some gotchas which caused a little head-scratching:
exit(0)in child script (
datareceived2.pl) terminated running of caller perl script, so I removed this.
datarecieved2.plused non-strict mode which meant variables were global and caused a little confusion, so I added
use strict;at the top of both scripts to point out those variables which needed to be localised through the
mykeyword. http://en.wikibooks.org/wiki/Perl_Programming/Functions#Important_note:_global_and_local_variables gave me good insight.
- use of
requireloads and executes the perl script once and once only whilst
doexecutes the perl script as many times as you call it. In my case, I needed
do. Thanks to http://soniahamilton.wordpress.com/2009/05/09/perl-use-require-import-and-do/