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Re: newbie hasher
by Zaxo (Archbishop) on Nov 20, 2003 at 05:18 UTC
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Probably the easiest way is to split each line and explicitly add the pair to the hash,
my %hosts;
{
local $_;
open my $fh, '<', '/path/to/data.file' or die $!;
while (<$fh>) {
my @pair = split;
$hosts{ $pair[0] } = $pair[1];
}
close $fh or die $!;
}
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Though I'm responding to Zaxo, my comment applies to most of the answers I see. With code doing a split, check that $pair[1] aka $ip is actually getting set to a defined value. Otherwise, your hash value may be undef on bad input but you won't get a warning about it until you actually try to use the hash value later on. Best to validate as you go:
while (<$fh>) {
chomp;
my ($host, $ip) = split;
warn("bad hosts line: $_"),next if !defined $ip;
$hosts{$host} = $ip;
}
Note that if you check defined($ip) the chomp is necessary, since otherwise $ip set to the empty string (taken from the empty string following the newline character).
If you use a regex to split up the line instead, make sure it actually requires both fields and check
if the match succeeds (which gets a little funky if you are using map):
%hosts = map {
if (/^(\w+)\s(.+)/) {
($1 => $2)
} else {
(warn "bad hosts line: $_")[1..0];
}
} <FILE>;
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Re: newbie hasher (No loops!)
by BrowserUk (Patriarch) on Nov 20, 2003 at 05:49 UTC
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#! perl -slw
use strict;
use Data::Dumper;
my %h = split ' ', do{ local $/; <DATA> };
print Dumper \%h;
__DATA__
host1 1.1.1.1
host2 2.2.2.2
host3 3.3.3.3
host4 4.4.4.4
Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
Hooray!
Wanted!
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Re: newbie hasher
by Anonymous Monk on Nov 20, 2003 at 05:19 UTC
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If your lines are simply host and IP separated by a space, then it's pretty simple:
open my $fh, "<input.dat" or die "Couldn't open file: $!";
my %hosts;
while (<$fh>) {
chomp;
my ($host, $ip) = split;
$hosts{$host} = $ip;
}
use Data::Dumper;
print Dumper \%hosts;
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Re: newbie hasher
by Roger (Parson) on Nov 20, 2003 at 05:32 UTC
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Or you could write a one-liner to transform the input file into a hash.
Method 1 - (map with 'short-circuit', now handles empty lines)
use strict;
use Data::Dumper;
# Uh, well spotted, typo fixed with the extra +
# which would have no effect anyway. :-)
# ysth suggested that putting () in map shortcircuts
# empty lines. It worked. Thanks. :-)
# Wow, even better, dropped that testing bit.
#my %hostlist = map { /^(\w+)\s(.*)/?($1,$2):() } (<DATA>);
my %hostlist = map { /^(\w+)\s(.*)/ } (<DATA>);
print Dumper(\%hostlist);
__DATA__
host1 1.1.1.1
host2 1.2.3.5
Method 2 - Better approach
use strict;
use Data::Dumper;
my %hostlist;
{
local $/;
%hostlist = <DATA> =~ /^(\w+)\s(.*)/gm;
}
print Dumper(\%hostlist);
__DATA__
host1 1.1.1.1
host2 1.2.3.5
Updated: added the 3rd method after seen jonadab's suggestion. Here's my solution of capturing a real host file.
Method 3 - Capture from the /etc/host file
use strict;
use Data::Dumper;
my %hosts;
while (<DATA>) {
next if /^\s*(?:#|$)/; # ignore comments and empty lines
/^([^\s#]+)\s+(.*)/; # capture ip address and names
$hosts{$_} = $1 foreach split /\s+/, $2;
}
print Dumper(\%hosts);
__DATA__
# IP Masq gateway:
192.168.0.80 pedestrian
# Primary desktop:
192.168.0.82 raptor1
# Family PC upstairs:
192.168.0.84 trex tyrannosaur family
# Domain servers:
205.212.123.10 dns1 brutus
208.140.2.15 dns2
156.63.130.100 dns3 cherokee
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By no means am I discounting the other methods, but I really like this one-liner due to my haphazzard knowledge of regex:
%hostlist = <DATA> =~ /^(\w+)+\s(.*)/gm;
This is exactly what I was looking for even though I was no where near explicit about what I wanted.
I'm already applying this method to a few more scripts. The map was cool too.
I am somewhat curious as to the extensive use of Data::Dumper instead of print-ing %hash?
Thanks all!
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I am somewhat curious as to the extensive use of Data::Dumper instead of print-ing %hash?
Just shows the structure better, and shows up any undefs, tabs, newlines, wide characters, unprintable characters, etc. that sneak into your data better.
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my %hotlist = map { m#\A(\S+)\s+(.*)\z#; $1 => $2 } <DATA>;
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my %hostlist = map { /^(\w+)\s(.*)/; $1 => $2 } (<DATA>);
should be....
my %hostlist = map { /^(\w+)\s+(.*)/; $1 => $2 } (<DATA>);
(extra + after the whitespace metachar)
davis
It's not easy to juggle a pregnant wife and a troubled child, but somehow I managed to fit in eight hours of TV a day.
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Re: newbie hasher
by davido (Cardinal) on Nov 20, 2003 at 05:35 UTC
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use strict;
use warnings;
my %hash = map { chomp; split /\s+/, $_, 2 } <DATA>;
print "$_, $hash{$_}\n" foreach keys %hash;
__DATA__
host1 1.1.1.1
host2 1.2.3.5
Fun huh? ;)
Dave
"If I had my life to live over again, I'd be a plumber." -- Albert Einstein
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Re: newbie hasher
by etcshadow (Priest) on Nov 20, 2003 at 05:24 UTC
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# assuming you've already opened your file...
while (my $line = <FILE>) {
chomp $line;
my ($host,$ip) = split(/\s+/,$line,2);
$hosts{$host} = $ip;
}
------------
:Wq
Not an editor command: Wq
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Close to perfect, IMO, except that I'd add a test for empty lines, like this:
my ($host,$ip) = split(/\s+/,$line,2) or next;
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Re: newbie hasher
by DrHyde (Prior) on Nov 20, 2003 at 09:06 UTC
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While I don't doubt that your file looks like that, it's not a regular hosts file. In /etc/hosts, each line has an IP followed by a name (and optionally more names), whereas you have a name followed by an IP. /etc/hosts can also have comments in it. To deal with a traditional /etc/hosts file ...
open(HOSTS, '/etc/hosts') || die("Out of cucumber error\n");
my %hosts;
while(<HOSTS>) {
s/#.*//;
next unless /(\S+)\s+(.*)/;
my $host = $1;
push @{$hosts{$host}}, split(/\s+/, $2);
}
use Data::Dumper;
print Dumper(\%hosts);
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Re: newbie hasher
by Coruscate (Sexton) on Nov 20, 2003 at 05:37 UTC
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open my $hosts, '<', 'hosts.txt' or die "open failed: $!";
my %hosts = map {
chomp; split /\s+/
} <$hosts>;
close $hosts or die "close failed: $!";
Update: Dope! Two people got maps in before me (somehow) lol
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Re: newbie hasher
by jonadab (Parson) on Nov 20, 2003 at 12:12 UTC
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my %hosts = map{
split /\s+/, $_, 2
}<DATA>; # Or substitute your favourite filehandle here.
__DATA__
host1 1.1.1.1
host2 1.2.3.5
Note, however, that the format you give is not the
standard format for hosts files. The usual format
is more like...
# IP Masq gateway:
192.168.0.80 pedestrian
# Primary desktop:
192.168.0.82 raptor1
# Family PC upstairs:
192.168.0.84 trex tyrannosaur family
# Domain servers:
205.212.123.10 dns1 brutus
208.140.2.15 dns2
156.63.130.100 dns3 cherokee
This is easy enough to read too...
open HOSTS, "</etc/hosts"; # Or "<C:\\WINDOWS\\hosts";
my %hosts = map{
my $ip, $hn, @hn;
if (not /^\s*#/) {
chomp; s/\s*#.*$//;
($ip, @hn) = split /\s+/, $_;
}
map { $_ => $ip }, @hn;
}<HOSTS>;
$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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Re: newbie hasher
by Art_XIV (Hermit) on Nov 20, 2003 at 13:58 UTC
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If you expect your input to be 'dirty', then regular expressions might serve you better:
use strict;
use Data::Dumper;
my %hosts;
while (<DATA>) {
chomp;
next if /^#/;
$hosts{$1} = $2
if /^(\w+)\s(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/;
warn "Garbage at line $. of DATA: $_\n" unless $1 and $2;
}
print Dumper(%hosts);
1;
__DATA__
host1 1.13.10.116 #comment
host2 21.90.30.31 #blah blah blah
host3 56.87.1.10
host4 13.16.17
#The following hosts are on network B
host5 57.98.18.10 #yadda yadda yadda
host6 106.10.3.12
Splits would be more efficient if you expect the input to be clean, though.
Hanlon's Razor - "Never attribute to malice that which can be adequately explained by stupidity"
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