update: Changed the regex to match the data provided by the OP.

my $high_id = 0;
open my $ID_FILE, "<", "path/to/file" or die $!;
while ( <$ID_FILE> ) {
    my ( $id ) = m/:(\d+):/; # extract first number from line
    $high_id = $id if $id > $high_id;
}
print "highest id found = $high_id\n";
[download]

Sorry for the lack of information guys, I'll show you the basic syntax of our printer config file.

M08_amvpss09_MEDIP :279:lp -damvpss09 >amvpss09.trace 2>&1

The number :279 is the identifier we need to locate and add by one.

There are over 700 unique numbers in no particular order, Are you guessing that this will need to be sorted by columns?

#!/usr/bin/perl

use strict;
use warnings;

my %prns;

for (<DATA>)
{
    my ( $num, $prn ) = split /\s/;
    $prns{$num} = $prn;
}

my @ord = sort { $b <=> $a } keys %prns;

print "Highest numbered printer is $prns{shift @ord}\n";

__DATA__
1 prt1
2 prt2
99 prt99
10 prt10
100 prt100
7 prt7
[download]

use strict;
use warnings;

my %prns;

for (<DATA>)
{
    my ( $printer, $num, $cmd ) = split /:/;
    $prns{$num} = $printer;
}

my @ord = sort { $b <=> $a } keys %prns;

print "Highest numbered printer is $prns{shift @ord}\n";

__DATA__
M08_amvpss09_MEDIP :275:lp -damvpss09
M07_amvpss09_MEDIP :279:lp -damvpss09
M09_amvpss09_MEDIP :278:lp -damvpss09
M01_amvpss09_MEDIP :2:lp -damvpss09
M04_amvpss09_MEDIP :1000:lp -damvpss09
[download]

Why would you do a full sort just to find the maximum value?

Its just what I though of first. You could also do:

use strict;
use warnings;
use List::Util qw(max);

my %prns;

while (<DATA>)
{
    my ( $printer, $num, $cmd ) = split /:/;
    $prns{$num} = $printer;
}

print "Highest numbered printer is $prns{max (keys %prns) }\n";
__DATA__
M08_amvpss09_MEDIP :275:lp -damvpss09
M07_amvpss09_MEDIP :279:lp -damvpss09
M09_amvpss09_MEDIP :278:lp -damvpss09
M01_amvpss09_MEDIP :2:lp -damvpss09
M04_amvpss09_MEDIP :1000:lp -damvpss09
[download]

Something line FunkyMonk's suggestion would work as well.
Ted
--
"That which we persist in doing becomes easier, not that the task itself has become easier, but that our ability to perform it has improved."
  --Ralph Waldo Emerson

So the first step is to provide a sample config file here ;)

perl -ne '$"<($_=(split(/:/, $_))[1]) and $"=$_;eof&&print$"' file.con
+f
[download]

Its a great command line usage. But it does NOT work if input data is negative numbers. Can you throw some light? -Thanks