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

I need to verify there is no duplicate UIDs in the /etc/passwd file. My plan was to sort the file by the UID, and then check for lines with UID = to previous line. Is this the best way? I was trying this code: 
#!/usr/bin/perl -w
#<SortPW2.pl> /etc/passwd sort by UID

$file="/etc/passwd";
my @array = do { local( @ARGV, $/ ) = $file ; <> } ;
#my @array = (
          #'555900:user:lee:0:23030',
          #'3520916:user:joe:0:20487',
          #'395284:user:richard:3:17557',
          #'807060:group:smith:0:20573',
          #'381940:home:kimble:1:625',
#);

my @sorted = map {$_->[0]}
             sort {$a->[1] <=> $b->[1] || $a->[1] cmp $b->[1]}
             map {[$_,(split':')[0]]} @array;

print "$_\n" for @sorted;

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The commented out code works, but the modification to source the array from /etc/passwd fails. Is it the line feeds? how would I remove them? Or is there a better way. All help appreciated. Thanx

Replies are listed 'Best First'.
Re: Sort passwd by UID
by moritz (Cardinal) on Apr 06, 2011 at 12:46 UTC
    Setting $/ to undef (via local) makes it read the whole file as a single string, and not line by line. Which is why your approach fails.
    My plan was to sort the file by the UID, and then check for lines with UID = to previous line. Is this the best way?

    Not necessarily. The common perl idiom for checking uniqueness is to iterate over all the values, and store the UID in a hash. If it existed before in the hash, it's not uniq. Consider: 

    my %uids;
while (my $line = <$filehandle>) {
   my $uid = # extract from $line;
   if ($uids{$uid)) {
       print "'$uid' is duplicate\n"
   } else {
      $uids{$uid} = 1;
   }
}

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    Perl 6 - second systems done right
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      Thanx, worked gr8.
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Re: Sort passwd by UID
by toolic (Bishop) on Apr 06, 2011 at 12:49 UTC
    You have slurped all your input lines into the 1st element of the @array variable. Here's how I would do it: 
    use warnings;
use strict;
use File::Slurp;

my $file  = '/etc/passwd';
my @lines = read_file($file);
chomp @lines;
my @sorted = map {$_->[0]}
             sort {$a->[1] <=> $b->[1] || $a->[1] cmp $b->[1]}
             map {[$_,(split':')[0]]} @lines;

print "$_\n" for @sorted;

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