matching a line from one file in another

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

Hello your holinesses,
As my moniker implies, I am new to perl. I am trying to take input from STDIN that looks like this:
xs029
xs030
xs031
xs032
xs034

see if these hosts exist in a file and print the line in the file if they do. The contents of the file I'm searching through looks like this:

xs029 Host Node 129.202.178.129 - - - - - 10.200.178.129
xs030 Host Node 129.202.178.130 - - - - - 10.200.178.130
xs031 Host Node 129.202.178.131 - - - - - 10.200.178.131

and finally, here is my code. For some reason when I run it , it just sits there doing nothing. Any help would be much appreciated!

$infile="hosts.txt";
open(INPUT, $infile) || die "Error opening $infile\n";
my @allhosts = <INPUT>;
foreach $approvhost (<STDIN>)
    {
    foreach $host (<@allhosts>)
        {
        if ($host =~ m/^$approvhost/)
            {
            print $host;
            }
        }
    }
[download]

Comment on matching a line from one file in another Download Code

Replies are listed 'Best First'.
Re: matching a line from one file in another by Fletch (Bishop) on Apr 14, 2006 at 14:42 UTC
The line `foreach $host (<@allhosts>)` is just wrong. The diamond operator is for reading from filehandles; it has nothing to do with iterating over an array. You wanted `for my $host ( @allhosts )`. Having said that, a better approach would be to rethink what you're doing and go at the problem another way. Read in the list of hosts from STDIN first and stash them in a hash (e.g. `my %want; while( <STDIN> ) { chomp; $want{$_} = 1 }`). Next read the lines of the other file and split off the first element; if that element `exists $want{ $ele }` then you print the line.	[reply] [d/l] [select]
Re^2: matching a line from one file in another by New_to_this_stuff (Initiate) on Apr 14, 2006 at 17:02 UTC
I think you are probably correct, a hash would be much cleaner. I will probably rewrite accordingly (good way to teach myself how to work with hashes), thanks.	[reply]
Re: matching a line from one file in another by davidrw (Prior) on Apr 14, 2006 at 14:54 UTC
You can also just use the *nix command-line utility `join` (it supports reading from STDIN) .. `join - hosts.txt # and type/paste in the input ./some_program \| join - hosts.txt # pipe the input in` [download]	[reply] [d/l] [select]
Re^2: matching a line from one file in another by Thelonius (Priest) on Apr 14, 2006 at 19:06 UTC
But remember that both input files need to be sorted. The examples were, but if not, you would have to sort them before the join.	[reply]
Re: matching a line from one file in another by Herkum (Parson) on Apr 14, 2006 at 14:38 UTC
You forgot to remove the \n character when they submitting the value to STDIN. Try this, `open(INPUT, "hosts.txt") \|\| die "Error opening 'hosts.txt'\n"; my @hosts = <INPUT>; while (<STDIN>) { chomp($_); foreach $host (@hosts) { if ($host =~ m/^$_/) { print "Host found: '$host'\n"; } } }` [download] As someone pointed out, the foreach should not be used with the STDIN and the brackets around @allhosts was wrong too. Fixed.	[reply] [d/l]
Re^2: matching a line from one file in another by New_to_this_stuff (Initiate) on Apr 14, 2006 at 17:00 UTC
Thank you for your speedy reply, it is now doing what I need it to!	[reply]
Re: matching a line from one file in another by davido (Cardinal) on Apr 14, 2006 at 15:54 UTC
As my moniker implies, I am new to perl. Being new to Perl is a temporary condition, and monikers generally are not. How would life go if your parents had named you "Newborn"? ;) Dave	[reply]
Re: matching a line from one file in another by cormanaz (Deacon) on Apr 15, 2006 at 00:20 UTC
I didn't test this, but I think what you want is: `$infile="hosts.txt"; open(INPUT, $infile) \|\| die "Error opening $infile\n"; my @allhosts = <INPUT>; close INPUT; while ($approvhost=<STDIN>) { chop($approvedhost); # or it won't partially match # your hosts entries becaus of # the training \n unless ($approvedhost) { last; } # so you can quit # with a null entry foreach $host (@allhosts) # omit the <> you're not # reading a file or stdin { if ($host =~ m/^$approvhost/) { print $host; } } }` [download]	[reply] [d/l]