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

Hi all,

Just a quickie. I think the answer is that the while loop is going through the file twice?

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Code that does what I expect, i.e. prints out the 42 lines of my passwd file, with array spaces swapped for <was :> and runs on $_:

#!/usr/bin/perl
use strict;
use warnings;

$" = '<was :>';

open PASSWD, "/etc/passwd"
  or die "Eh? ($!)";


while (<PASSWD>) {
my @passwds = split /:/;
print "@passwds";
}

[download]

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This now only prints 21 lines? I am not sure why? It misses the odd ones. 

#!/usr/bin/perl
use strict;
use warnings;

$" = '<was :>';

open PASSWD, "/etc/passwd"
  or die "Eh? ($!)";

while (<PASSWD>) {
my @passwds = split /:/, <PASSWD>;
print "@passwds";
}

[download]
Walking the road to enlightenment... I found a penguin and a camel on the way..... Fancy a yourname@perl.me.uk? Just ask!!!

Replies are listed 'Best First'.
Re: Understanding split in a while loop
by saskaqueer (Friar) on Feb 28, 2005 at 12:46 UTC 
    while (<PASSWD>) {
    my @passwds = split /:/, <PASSWD>;
}

    [download]

    Note that you've used <PASSWD> twice. This will skip the even-numbered lines of the file, not the odd-numbered. This is because you read a second line from the file each time inside the loop, splitting on that value. Therefore, your first line that is read from the file (read into $_ in the while() loop) is more or less being discarded.

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[d/l]
[select]

      I thought that was it. Thanks. So it discards the odd numbered ones, i.e. line 1 etc.

      Thanks.

      Walking the road to enlightenment... I found a penguin and a camel on the way..... Fancy a yourname@perl.me.uk? Just ask!!!
[reply]

        It doesn't discard them; it places them into $_ but you ignore it.</pedant>

[reply]
[d/l]

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