Greping an array obtained through NET:TELNET - perl

Question

I'm writing a Munin-Pluging and I like to capture the screen output from a telnet session.
The output of such a session looks as follows:
...
0x00017 0x41b3f340 BPING 0 0 0 0 198 132 330
0x00018 0x41b47340 CHKFAILED 0 0 0 0 198 132 330
0x00026 0x41b4f340 CIP 0 0 0 0 370 264 634
0x0001e 0x41b57340 CONTROL 0 1 0 0 3876 2178 6054
0x01014 0x41b5f340 UNETSRVR 0 0 0 1 296 198 494
0x00037 0x41b67340 ---- 0 0 0 0 198 132 330
0x00000 0x43b67450 ---- 0 0 0 0 0 0 0
0x00000 0x4bb67450 ---- 0 0 0 0 5084 4224 9308
0x00000 0x49367450 ---- 0 0 0 0 14742 4158 18900
-------------------------------------------------------------------------------------------
SUMMARY : 2 40 5 7 4898229 2728176 7626405
This script extract the screen content into an array (#lines).
#!/usr/bin/perl
use Net::Telnet ();
use strict;
use warnings;
my $t = new Net::Telnet (Timeout => 10);
$t->port(777);
$t->open("192.168.0.1");
$t->buffer_empty;
my #lines = $t->waitfor(match =>"m/.* SUMMARY : .* \n/");
my #gagu = grep { "$_" =~ /^.*BPING.*\n/ } #lines;
print #gagu;
Of what type is the array #lines?
Why do I always get the whole
content from grep and not a filtered line?
Is the array i got from net:telnet different from other arrays?
Yes, I'm new to Perl.

Answer 1

I am not familiar with this module and what it does, but I assume it gives you some sort of return value similar to what you have stated.
If you are getting all the lines in your #gagu array, that can be either that your data in the #lines array consists of just one line, or that the grep fails.
For example, #lines may contain the string:
"foo bar baz\nfoo1 bar1 baz1\n";
and not, as you expect
"foo bar baz\n";
"foo1 bar1 baz1\n";
Your grep statement probably works as expected, though you might want to consider:
Not quoting $_, since that serves no purpose.
Not using $_ at all, since that is the default variable it is not needed (except for clarity) to use it.
Not using anchors ^ and \n, because they are redundant.
For example, ^.* matches any string, anywhere. Using it to simply match a string is redundant. Ending the regex with .*\n is redundant, because all it says is "match any character except newline until we find a newline". Assuming you have newlines, it does nothing. Assuming you don't, it gives you a false negative. All you need for this match is /BPING/. So here's what your code might look like:
use Data::Dumper;
my #lines = $t->waitfor(match =>"m/ SUMMARY :/");
my #gagu = grep /BPING/, #lines;
print Dumper \#gagu;
If you want to see whitespace printed out visibly, you can use the $Data::Dumper::Useqq variable:
$Data::Dumper::Useqq = 1;
print Dumper \#gagu;
Printing variables is a very good debugging tool.