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

Hello,

I am doing something rather simple - iterating over the lines from <> and splitting each one into words. What I can't seem to figure out how to do, is grab the first two words from the first line, and then continue on as usual. In other words, I want to my $first_line = <>; my ($word1, $word2) = split /\s+/, $first_line; while(<>){...} but still have the rest of $first_line be processed in the wile(<>).

Am I missing something obvious?

(Oh, I wouldn't want to slurp the whole thing into RAM first, as the input can get rather largish)

Replies are listed 'Best First'.
Re: "uhshifting" the diamond?
by PodMaster (Abbot) on Oct 21, 2003 at 00:36 UTC
    `perldoc perlvar' => $. 
    while(<>){
    if( $. == 1 ){
        warn "i'm splitting";
        ...
    }
    ...
}

    [download]

    MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
    I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
    ** The third rule of perl club is a statement of fact: pod is sexy.

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Re: "uhshifting" the diamond?
by pzbagel (Chaplain) on Oct 21, 2003 at 00:46 UTC

    How about a do..while() so that the read happens at the end of the loop instead of the beginning: 

    #!/usr/bin/perl -w
 
use strict;
 
$_=<DATA>;
(my ($first, $second), $_) = split(/\s+/, $_, 3);

print "first: $first\n";
print "second: $second\n";

do{
print "rest: $_";
} while (<DATA>);
 
__DATA__
This is line one!
This is line two!
This is line three!
This is line four!
This is line five!

    [download]

    Outputs: 

    first: This
second: is
rest: line one!
rest: This is line two!
rest: This is line three!
rest: This is line four!
rest: This is line five!

    [download]

    HTH

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Re: "uhshifting" the diamond?
by Abigail-II (Bishop) on Oct 21, 2003 at 09:58 UTC 
    my $first_line = <>;
my ($word1, $word2) = split /\s+/ => $first_line;
$_ = $first_line;
while (1) {
    # Your loop.
    $_ = <> err last;   # Defined-or!
}

    [download]

    Abigail

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Re: "uhshifting" the diamond?
by Limbic~Region (Chancellor) on Oct 21, 2003 at 00:38 UTC
    glwtta,
    If this were a regular file, you could seek back to the beginning of the file. See perldoc -f seek. PodMaster was gracious enough to point out in a /msg that this would not work on a tty or a pipe.

    So this leaves handling the first line differently. This can be accomplished using a "flag" or using $. as PodMaster pointed out. That pretty makes this post pointless other than to show what you could do if this was a regular file.

    Cheers - L~R

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Re: "uhshifting" the diamond?
by delirium (Chaplain) on Oct 21, 2003 at 02:43 UTC
    You could move the meat of the while loop to another place, like so: 

    sub some_function {
  # do stuff with $_
}

my ($word1, $word2) = split /\s+/,<>;
&some_function;            # $_ is the first line
&some_function while (<>); # $_ cycles through rest of file

    [download]

    ...and if you dislike egregiously abusing $_, you can throw in explicit variables in some_function.

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