[OT] Help with Perl Script

[Dan Track]

Hi,

I appreciate that this is off-topic and wholly understand if I don't
get an answer, although one would really appreciate it if I do get an
answer :)

Basically to improve my perl scripting, I've given myself a challenge
where I would like to order the users in the passwd file by uid, I
could do this in another language but I'm focused on improving my perl
scripting. The script I've written so far is below, I've managed to
figure out hashes and have read in the file and created a hash of
hashes. It's after this that I'm stuck, I'm struggling to order the
hash of hashes by uid and then print the ordered list out? Can someone
please help me to finish this off? I'm trying to avoid using perl
modules as I want to improve my scripting ability.

#!/usr/bin/perl -w

use strict;

my ( $login, $p, $uid, $gid, $gecos, $dir, $s );
   my $k;
   my $v;
   my $key;
   my $ip;
   my $value;
   my @sorted=();

my @uid=();

my %HoH = ();

my $file='/etc/passwd';

open( PASSWD, "< $file" ) or die "Can't open $file : $!";

while( <PASSWD> ) {
            ( $login, $p, $uid, $gid, $gecos, $dir, $s ) = split( ':' );

$HoH{ $login }{ 'login' } = $login;
            $HoH{ $login }{ 'p' } = $p;
            $HoH{ $login }{ 'uid' } = $uid;
            $HoH{ $login }{ 'gid' } = $gid;
            $HoH{ $login }{ 'gecos' } = $gecos;
            $HoH{ $login }{ 'dir' } = $dir;
            $HoH{ $login }{ 's' } = $s;
            #print "$login\n";
        }

close PASSWD;

#while (($k,$v) = each %HoH) {
#   print "While Loop: $k\n";
#}

#foreach $ip (keys %HoH) {
#   print "First For:  $ip\n";
#    while (($key, $value) = each %{ $HoH{$ip} } ) {
#        print "$key = $value \n";
#    }
#   print "\n";
#}

#while ( ($k, $v) = each %HoH ) {
#    print "$k: \n";
#    while ( ($key, $value) = each %$v ) {
#        print "$key=$value ";
#    }
#    print "\n";
#}

#for $k ( sort keys %HoH ) {
#    print "$k: ";
#    for $v ( sort keys %{ $HoH{$k} } ) {
#         print "$v=$HoH{$k}{$v} ";
#    }
#    print "\n";
#}

#@sorted = sort { $HoH{$a} cmp $HoH{$b} } keys %HoH;
#print "@sorted\n";

#foreach my $sorted ( sort { $HoH{$a}->{"uid"} cmp $HoH{$b}->{"uid"} }
keys %HoH)
foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
{
print STDOUT "$HoH{$sorted}\n"
}

Thank in advance for any help.

Dan

[Dan Track]

Hi,

I appreciate that this is off-topic and wholly understand if I don't
get an answer, although one would really appreciate it if I do get an
answer :)

Basically to improve my perl scripting, I've given myself a challenge
where I would like to order the users in the passwd file by uid, I
could do this in another language but I'm focused on improving my perl
scripting. The script I've written so far is below, I've managed to
figure out hashes and have read in the file and created a hash of
hashes. It's after this that I'm stuck, I'm struggling to order the
hash of hashes by uid and then print the ordered list out? Can someone
please help me to finish this off? I'm trying to avoid using perl
modules as I want to improve my scripting ability.

#!/usr/bin/perl -w

use strict;

my ( $login, $p, $uid, $gid, $gecos, $dir, $s );
  my $k;
  my $v;
  my $key;
  my $ip;
  my $value;
  my @sorted=();

my @uid=();

my %HoH = ();

my $file='/etc/passwd';

open( PASSWD, "< $file" ) or die "Can't open $file : $!";

while( <PASSWD> ) {
           ( $login, $p, $uid, $gid, $gecos, $dir, $s ) = split( ':' );

$HoH{ $login }{ 'login' } = $login;
           $HoH{ $login }{ 'p' } = $p;
           $HoH{ $login }{ 'uid' } = $uid;
           $HoH{ $login }{ 'gid' } = $gid;
           $HoH{ $login }{ 'gecos' } = $gecos;
           $HoH{ $login }{ 'dir' } = $dir;
           $HoH{ $login }{ 's' } = $s;
           #print "$login\n";
       }

close PASSWD;

#while (($k,$v) = each %HoH) {
#   print "While Loop: $k\n";
#}

#foreach $ip (keys %HoH) {
#   print "First For:  $ip\n";
#    while (($key, $value) = each %{ $HoH{$ip} } ) {
#        print "$key = $value \n";
#    }
#   print "\n";
#}

#while ( ($k, $v) = each %HoH ) {
#    print "$k: \n";
#    while ( ($key, $value) = each %$v ) {
#        print "$key=$value ";
#    }
#    print "\n";
#}

#for $k ( sort keys %HoH ) {
#    print "$k: ";
#    for $v ( sort keys %{ $HoH{$k} } ) {
#         print "$v=$HoH{$k}{$v} ";
#    }
#    print "\n";
#}

#@sorted = sort { $HoH{$a} cmp $HoH{$b} } keys %HoH;
#print "@sorted\n";

#foreach my $sorted ( sort { $HoH{$a}->{"uid"} cmp $HoH{$b}->{"uid"} }
keys %HoH)
foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
{
print STDOUT "$HoH{$sorted}\n"
}

Thank in advance for any help.

Dan

[Bruno Wolff III]

On Wed, Apr 21, 2010 at 10:20:27 +0100,
  Dan Track  wrote:
> Basically to improve my perl scripting, I've given myself a challenge
> where I would like to order the users in the passwd file by uid, I
> could do this in another language but I'm focused on improving my perl
> scripting. The script I've written so far is below, I've managed to
> figure out hashes and have read in the file and created a hash of
> hashes. It's after this that I'm stuck, I'm struggling to order the
> hash of hashes by uid and then print the ordered list out? Can someone
> please help me to finish this off? I'm trying to avoid using perl
> modules as I want to improve my scripting ability.

It looks like you are doing string comparisons on the uid. I think you
might want to try <=> instead of cmp.

[Norman Gaywood]

On Wed, Apr 21, 2010 at 09:21:30AM +0100, Dan Track wrote:
> hashes. It's after this that I'm stuck, I'm struggling to order the
> hash of hashes by uid and then print the ordered list out? Can someone

[snip]
> foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)

cmp is a string comparison. You probably want to sort numerically on the
uid. So replace 'cmp' with '<=>'

Perhaps that is the problem?

[Dan Track]

On Wed, Apr 21, 2010 at 1:30 PM, Norman Gaywood  wrote:
> On Wed, Apr 21, 2010 at 09:21:30AM +0100, Dan Track wrote:
> > hashes. It's after this that I'm stuck, I'm struggling to order the
> > hash of hashes by uid and then print the ordered list out? Can someone
>
> [snip]
> > foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
>
> cmp is a string comparison. You probably want to sort numerically on the
> uid. So replace 'cmp' with '<=>'
>
> Perhaps that is the problem?

Hi,

Thanks for that, although it didn't work at least I think so.

foreach my $sorted ( sort { $HoH{$a}->{"uid"} <=> $HoH{$b}->{"uid"} } keys %HoH)
{
print STDOUT "$HoH{$sorted}\n"
}

and all I get out is:

perl sort.pl
HASH(0x89de3d0)
HASH(0x8a05d40)
HASH(0x8a05dd0)
HASH(0x8a05e60)
HASH(0x8a05ef0)
HASH(0x8a05f80)
HASH(0x8a06010)
HASH(0x8a060a0)
HASH(0x8a06130)
HASH(0x8a061c0)
HASH(0x8a06250)
HASH(0x8a062e0)
HASH(0x8a06370)
HASH(0x8a06400)
HASH(0x8a0fd70)
HASH(0x8a0fe90)
HASH(0x8a101f0)
HASH(0x8a10040)
HASH(0x8a10790)
HASH(0x8a100d0)
HASH(0x8a10160)
HASH(0x8a10700)
HASH(0x8a10430)
HASH(0x8a0ff20)
HASH(0x8a10550)
HASH(0x8a10310)
HASH(0x8a0ffb0)
HASH(0x8a103a0)
HASH(0x8a0fe00)
HASH(0x8a104c0)
HASH(0x8a105e0)
HASH(0x8a10670)
HASH(0x8a10280)

Any thoughts on this?

Thanks
Dan

[Norman Gaywood]

On Wed, Apr 21, 2010 at 04:12:06PM +0100, Dan Track wrote:
> On Wed, Apr 21, 2010 at 1:30 PM, Norman Gaywood  wrote:
> > On Wed, Apr 21, 2010 at 09:21:30AM +0100, Dan Track wrote:
> > > hashes. It's after this that I'm stuck, I'm struggling to order the
> > > hash of hashes by uid and then print the ordered list out? Can someone
> >
> > [snip]
> > > foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
> >
> > cmp is a string comparison. You probably want to sort numerically on the
> > uid. So replace 'cmp' with '<=>'
> foreach my $sorted ( sort { $HoH{$a}->{"uid"} <=> $HoH{$b}->{"uid"} } keys %HoH)
> {
> print STDOUT "$HoH{$sorted}\n"
> }
> and all I get out is:
>
> perl sort.pl
> HASH(0x89de3d0)
> HASH(0x8a05d40)

[snip]

$HoH{$sorted} is a reference to a hash. $HoH{$a}{uid} (or in
long hand $HoH{$a}->{"uid"}) should print out the uid numbers.

[Norman Gaywood]

On 22 April 2010 01:26, Norman Gaywood  wrote:
> On Wed, Apr 21, 2010 at 04:12:06PM +0100, Dan Track wrote:
> > On Wed, Apr 21, 2010 at 1:30 PM, Norman Gaywood  wrote:
> > > On Wed, Apr 21, 2010 at 09:21:30AM +0100, Dan Track wrote:
> > > > hashes. It's after this that I'm stuck, I'm struggling to order the
> > > > hash of hashes by uid and then print the ordered list out? Can someone
> > >
> > > [snip]
> > > > foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
> > >
> > > cmp is a string comparison. You probably want to sort numerically on the
> > > uid. So replace 'cmp' with '<=>'
> > foreach my $sorted ( sort { $HoH{$a}->{"uid"} <=> $HoH{$b}->{"uid"} } keys %HoH)
> > {
> > print STDOUT "$HoH{$sorted}\n"
> > }
> > and all I get out is:
> >
> > perl sort.pl
> > HASH(0x89de3d0)
> > HASH(0x8a05d40)
>
> [snip]
>
> $HoH{$sorted} is a reference to a hash. $HoH{$a}{uid} (or in
> long hand $HoH{$a}->{"uid"}) should print out the uid numbers.

That should be $HoH{$sorted}{uid}

[jack craig]

google is perl's best friend, google, 'perl sort arrays' ...

good luck, jackc...

On 04/21/2010 01:21 AM, Dan Track wrote:
> Hi,
>
> I appreciate that this is off-topic and wholly understand if I don't
> get an answer, although one would really appreciate it if I do get an
> answer :)
>
> Basically to improve my perl scripting, I've given myself a challenge
> where I would like to order the users in the passwd file by uid, I
> could do this in another language but I'm focused on improving my perl
> scripting. The script I've written so far is below, I've managed to
> figure out hashes and have read in the file and created a hash of
> hashes. It's after this that I'm stuck, I'm struggling to order the
> hash of hashes by uid and then print the ordered list out? Can someone
> please help me to finish this off? I'm trying to avoid using perl
> modules as I want to improve my scripting ability.
>
> #!/usr/bin/perl -w
>
> use strict;
> my ( $login, $p, $uid, $gid, $gecos, $dir, $s );
> my $k;
> my $v;
> my $key;
> my $ip;
> my $value;
> my @sorted=();
>
> my @uid=();
>
> my %HoH = ();
>
> my $file='/etc/passwd';
>
> open( PASSWD, "<  $file" ) or die "Can't open $file : $!";
>
> while(<PASSWD>  ) {
>              ( $login, $p, $uid, $gid, $gecos, $dir, $s ) = split( ':' );
>          $HoH{ $login }{ 'login' } = $login;
>          $HoH{ $login }{ 'p' } = $p;
>          $HoH{ $login }{ 'uid' } = $uid;
>          $HoH{ $login }{ 'gid' } = $gid;
>          $HoH{ $login }{ 'gecos' } = $gecos;
>          $HoH{ $login }{ 'dir' } = $dir;
>          $HoH{ $login }{ 's' } = $s;
>          #print "$login\n";
>      }
>
>      close PASSWD;
>
> #while (($k,$v) = each %HoH) {
> #   print "While Loop: $k\n";
> #}
>
> #foreach $ip (keys %HoH) {
> #   print "First For:  $ip\n";
> #    while (($key, $value) = each %{ $HoH{$ip} } ) {
> #        print "$key = $value \n";
> #    }
> #   print "\n";
> #}
>
> #while ( ($k, $v) = each %HoH ) {
> #    print "$k: \n";
> #    while ( ($key, $value) = each %$v ) {
> #        print "$key=$value ";
> #    }
> #    print "\n";
> #}
>
> #for $k ( sort keys %HoH ) {
> #    print "$k: ";
> #    for $v ( sort keys %{ $HoH{$k} } ) {
> #         print "$v=$HoH{$k}{$v} ";
> #    }
> #    print "\n";
> #}
>
> #@sorted = sort { $HoH{$a} cmp $HoH{$b} } keys %HoH;
> #print "@sorted\n";
>
> #foreach my $sorted ( sort { $HoH{$a}->{"uid"} cmp $HoH{$b}->{"uid"} }
> keys %HoH)
> foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
> {
> print STDOUT "$HoH{$sorted}\n"
> }
>
> Thank in advance for any help.
>
> Dan

[Dan Track]

On Wed, Apr 21, 2010 at 4:41 PM, Norman Gaywood  wrote:
> On 22 April 2010 01:26, Norman Gaywood  wrote:
> > On Wed, Apr 21, 2010 at 04:12:06PM +0100, Dan Track wrote:
> > > On Wed, Apr 21, 2010 at 1:30 PM, Norman Gaywood  wrote:
> > > > On Wed, Apr 21, 2010 at 09:21:30AM +0100, Dan Track wrote:
> > > > > hashes. It's after this that I'm stuck, I'm struggling to order the
> > > > > hash of hashes by uid and then print the ordered list out? Can someone
> > > >
> > > > [snip]
> > > > > foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys %HoH)
> > > >
> > > > cmp is a string comparison. You probably want to sort numerically on the
> > > > uid. So replace 'cmp' with '<=>'
> > > foreach my $sorted ( sort { $HoH{$a}->{"uid"} <=> $HoH{$b}->{"uid"} } keys %HoH)
> > > {
> > > print STDOUT "$HoH{$sorted}\n"
> > > }
> > > and all I get out is:
> > >
> > > perl sort.pl
> > > HASH(0x89de3d0)
> > > HASH(0x8a05d40)
> >
> > [snip]
> >
> > $HoH{$sorted} is a reference to a hash. $HoH{$a}{uid} (or in
> > long hand $HoH{$a}->{"uid"}) should print out the uid numbers.
>
> That should be $HoH{$sorted}{uid}
>
> --

Fantastic, you're a star :)

One last point how can I print all the associated deatils attached to
that uid i.e username, home dir etc and then cycle through for every
uid and print the same information for each respective uid? The uid's
need to be in order i.e something like

uid: 0, username: root etc...
uid 50, username: mysql etc...

Many many thanks
Dan

[Jake Peavy]

On Wed, Apr 21, 2010 at 4:21 AM, Dan Track  wrote:
> Hi,

Hey
> I appreciate that this is off-topic and wholly understand if I don't
> get an answer, although one would really appreciate it if I do get an
> answer :)

Can you please mark as OT in the subject next time?  That way anyone not
interested in non-Fedora specific questions can easily filter off topic
subjects out.

Basically to improve my perl scripting, I've given myself a challenge
> where I would like to order the users in the passwd file by uid, I
> could do this in another language but I'm focused on improving my perl
> scripting. The script I've written so far is below, I've managed to
> figure out hashes and have read in the file and created a hash of
> hashes. It's after this that I'm stuck, I'm struggling to order the
> hash of hashes by uid and then print the ordered list out? Can someone
> please help me to finish this off? I'm trying to avoid using perl
> modules as I want to improve my scripting ability.

sure, I'll provide some tips.
> #!/usr/bin/perl -w

-w is deprecated.  use warnings; instead
> use strict;

very good.  always use strict;
> my ( $login, $p, $uid, $gid, $gecos, $dir, $s );
>   my $k;
>   my $v;
>   my $key;
>   my $ip;
>   my $value;
>   my @sorted=();
>
> my @uid=();

this is a common error for ex-C/Java programmers, however in Perl there's no
need to predefine variables.  In fact, variables should be defined only in
their smallest possible scope.  This happens naturally if you define them as
you use them.
> my %HoH = ();

this is an ok name for learning, but in real scripts use a name that
describes the contents, rather than the structure.

my $file='/etc/passwd';
> open( PASSWD, "< $file" ) or die "Can't open $file : $!";

new method is 3-argument open, with lexically scoped filehandle:
open( my $passwd, '<', $file ) or die "Can't open '$file': $!";
> while( <PASSWD> ) {

this reads from the filehandle until eof, putting the results in $_.  It is
convenient to use $_, but it is usually advisable to create a new lexically
scoped variable.

while( my $line = <$passwd> ) {
>        ( $login, $p, $uid, $gid, $gecos, $dir, $s ) = split( ':' );

if these hadn't been pre-defined, this line would read as follows and would
keep $login, $p, etc scoped to this while block

my ($login,$p,$uid,$gid,$gecos,$dir,$s) = split ':', $line;
>        $HoH{ $login }{ 'login' } = $login;
>        $HoH{ $login }{ 'p' } = $p;
>        $HoH{ $login }{ 'uid' } = $uid;
>        $HoH{ $login }{ 'gid' } = $gid;
>        $HoH{ $login }{ 'gecos' } = $gecos;
>        $HoH{ $login }{ 'dir' } = $dir;
>        $HoH{ $login }{ 's' } = $s;
>        #print "$login\n";
>    }

This structure works well if you wanted to look up the characteristics of a
given $login as hash access is great for lookups.  but if you wanted to just
reorder all of them, maybe an array of hashes would be better?  just a
thought.
>    close PASSWD;
>
> #while (($k,$v) = each %HoH) {
> #   print "While Loop: $k\n";
> #}
>
> #foreach $ip (keys %HoH) {
> #   print "First For:  $ip\n";
> #    while (($key, $value) = each %{ $HoH{$ip} } ) {
> #        print "$key = $value \n";
> #    }
> #   print "\n";
> #}
>
> #while ( ($k, $v) = each %HoH ) {
> #    print "$k: \n";
> #    while ( ($key, $value) = each %$v ) {
> #        print "$key=$value ";
> #    }
> #    print "\n";
> #}
>
> #for $k ( sort keys %HoH ) {
> #    print "$k: ";
> #    for $v ( sort keys %{ $HoH{$k} } ) {
> #         print "$v=$HoH{$k}{$v} ";
> #    }
> #    print "\n";
> #}
>
> #@sorted = sort { $HoH{$a} cmp $HoH{$b} } keys %HoH;
> #print "@sorted\n";
>
> #foreach my $sorted ( sort { $HoH{$a}->{"uid"} cmp $HoH{$b}->{"uid"} }
> keys %HoH)
> foreach my $sorted ( sort { $HoH->{$a}{uid} cmp $HoH->{$b}{uid} } keys
> %HoH)
> {
> print STDOUT "$HoH{$sorted}\n"
> }

as others have mentioned, to perform numeric comparisons use the "spaceship"
operator: <=>

now, note how many hash accesses your loop performs.  each time the sort
wishes to compare two values, it must perform two nested hash lookups.  As
your Perl improves, you will learn how to make this sort more efficient -
one common method is called the Schwartzian Transform.  (No relation to
Spaceballs)
> Thank in advance for any help.http://fedoraproject.org/wiki/Mailing_list_guidelines

Hope my comments helped.  Welcome to Perl.

[Jake Peavy]

On Wed, Apr 21, 2010 at 12:34 PM, Jake Peavy  wrote:
> On Wed, Apr 21, 2010 at 4:21 AM, Dan Track  wrote:
> > Hi,
>
> Hey
> > I appreciate that this is off-topic and wholly understand if I don't
> > get an answer, although one would really appreciate it if I do get an
> > answer :)
>
> Can you please mark as OT in the subject next time?  That way anyone not
> interested in non-Fedora specific questions can easily filter off topic
> subjects out.

LOL my bad....

[Dave Cross]

On 21 April 2010 09:21, Dan Track  wrote:
> Hi,
>
> I appreciate that this is off-topic and wholly understand if I don't
> get an answer, although one would really appreciate it if I do get an
> answer :)
>
> Basically to improve my perl scripting, I've given myself a challenge
> where I would like to order the users in the passwd file by uid,

You've already got plenty of good advice in this thread, but I thought
you might be interested in seeing just how short the program can be if
you use a lot of Perl's features.

#!/usr/bin/perl

use strict;
  use warnings;

@ARGV = '/etc/passwd';

print sort { (split /:/, $a)[2] <=> (split /:/, $b)[2] } <>;

I probably wouldn't use something _quite_ this cryptic in production code.

Cheers,

Dave...

[Dave Ihnat]

On Fri, Apr 23, 2010 at 09:06:45AM +0100, Dave Cross wrote:
> I probably wouldn't use something _quite_ this cryptic in production code.

Oh, that wouldn't be a problem *IF* you commented the he11 out of it and
bracketed the code with "DON'T CHANGE THIS IF YOU DON'T UNDERSTAND IT"
comments.

IF tests showed this was much more efficient, that is.  If it isn't,
then cryptic isn't worth it.

Cheers,
--
    Dave Ihnat
    [e-mail]