zuinc has asked for the wisdom of the Perl Monks concerning the following question:

I have a file containing the output after pinging several IP addresses. For example, the first line is "12.34.56.78 is alive" and line 2 is "no answer from 12.34.56.79" and so on. I am trying to print only those lines that contain the words "is alive." I tried several things including grep and if-else statements but only want those lines containing "is alive" to print to a separate file & am having no luck. Heres what I have so far: 
# Create a list of all possible IP addresses within subnet
open(ALLIP, ">allip.list") || die "Unable to create file: allip.list\n
+";
for ($i=0; $i<=20; $i++) {
        print ALLIP "$ip_subnet.$i\n";
        }
close(ALLIP);

open(ALLIP, "allip.list") || die "Unable to open file: allip.list\n";
open(PINGALLIP, ">pingallip.list") || die "Unable to open file: pingal
+lip.list";
while (<ALLIP>) {
        chomp;
        system("ping $_ >>pingallip.list") && "Unable to create file: 
+pingallip.
list";
        }
close(ALLIP);
close(PINGALLIP);

open(ALIVEIP, ">aliveip.list");
close(ALIVEIP);
open(ALIVEIP, "aliveip.list");
open(PINGALLIP, "pingallip.list") || die "Unable to open file: pingall
+ip.list";
while (<PINGALLIP>) {
   if (/is alive/) {
                chomp;
                print ALIVEIP $_;
        }
}
close(PINGALLIP);

[download]
Any help would be greatly appreciated. The idea of using the IP module has already been mentioned to me but I am also using this as an excuse to improve my perl skills. =) Thanks.

Zuinc

Replies are listed 'Best First'.
Re: Printing matched lines
by perlplexer (Hermit) on Apr 09, 2002 at 18:35 UTC
    grep 'is alive' log.dat > out.dat

    Or if you really want to do this in Perl: 
    # Assuming file name is in $ARGV[0]
while(<>){
   print if /is alive/;
}

    [download]
    or just

    perl -ne "print if /is alive/" log.dat > out.dat

    --perlplexer
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Re: Printing matched lines
by Kanji (Parson) on Apr 09, 2002 at 18:39 UTC

    If your code is cut-n-pasted, part of your problem lies in the snippet below, where you re-open the file you plan on printing to, but as read-only.

    open(ALIVEIP, ">aliveip.list");
close(ALIVEIP);
open(ALIVEIP, "aliveip.list");

    [download]

    Also, do you really need to chomp when reading from <PINGALLIP>? If you want each message printed on a line by itself, you can just use...

    while ( my $line = <PINGALLIP>) {
   print ALIVEIP $line if $line =~ /is alive/;
}

    [download]

        --k.


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Re: Printing matched lines
by emilford (Friar) on Apr 09, 2002 at 18:38 UTC
    I think your best bet would be to use Perl's match operator, but then again one of the other monks might have a better solution (I'm still learning!). I just setup a little test text file and wrote a few lines of code (below) and it does what you were asking for. 
    Text file
---------------------------------------
1234567 is alive
12345678 is not alive
123456789 is alive<br><br>

Code
---------------------------------------
#! /usr/bin/perl -w
use strict;

open(FILE, ">test.txt") || die "Unable to open file: $!";
chomp (my @input = <FILE>); # store lines in array, removing CRLF
close(FILE);

foreach my $line (@input) {
   if($line =~ m/is alive/) {
      print "$line\n";
   }
}

Output
-------------------------------------
1234567 is alive
123456789 is alive

    [download]
    Hope this helps!! -Eric
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Re: Printing matched lines
by Zaxo (Archbishop) on Apr 09, 2002 at 18:36 UTC

    while is not setting $_ for you. in

    while (<PINGALLIP>) {
   if (/is alive/) {
      chomp;
      print ALIVEIP $_;
   }
}

    [download]
    Try this instead:
    /is alive/ and print ALIVEIP for <PINGALLIP>;

    [download]
    If the match is true then print $_ for all lines. I omitted chomp since the record delimiters will probably be handy in the file.

    After Compline,
    Zaxo

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Re: Printing matched lines
by dug (Chaplain) on Apr 09, 2002 at 18:36 UTC
    change: 
    while (<PINGALLIP>) {
   if (/is alive/) {
                chomp;
                print ALIVEIP $_;
        }
}

    [download]
    to: 
    while (<PINGALLIP>) {
   if ($_ =~ /is alive/) {
                chomp;
                print ALIVEIP $_;
        }
}

    [download]
    That will apply the m// operator to magic variable $_, which is the current line of your while loop.
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