problem with passing variables
I'm not sure if this is the right list for this, so bear with me. If it
isn't I'll be glad to post it on the correct one.
I've got a problem with passing variables to a SQL server inside a CGI
script. My code is like this:
my $begin_time = 2011-11-16 11:00:00;
my $end_time = 2011-11-16 12:00:00;
my $dbh = DBI-connect('dbi:mysql:database=embdev', 'user', 'password');
my $sql = q/SELECT * FROM events WHERE date BETWEEN $begin_time and
$end_time/;
my $sth = $dbh-prepare($sql);
$sth-execute();
I'm not sure why it's not using the the variables, can someone point out
what I'm doing wrong?
-
Mark Haney
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Re: problem with passing variables
Mark,
I'm kind of new with perl, but from what I see, you're using a single
quote when defining $sql, and it should be qq for the interpolated string.
With the single quote (q) it is a literal. Hope this helps.
On Friday, December 30, 2011 11:17:30 AM Mark Haney wrote:
I'm not sure if this is the right list for this, so bear with me. If it
isn't I'll be glad to post it on the correct one.
I've got a problem with passing variables to a SQL server inside a CGI
script. My code is like this:
my $begin_time = 2011-11-16 11:00:00;
my $end_time = 2011-11-16 12:00:00;
my $dbh = DBI-connect('dbi:mysql:database=embdev', 'user', 'password');
my $sql = q/SELECT * FROM events WHERE date BETWEEN $begin_time and
$end_time/;
my $sth = $dbh-prepare($sql);
$sth-execute();
I'm not sure why it's not using the the variables, can someone point out
what I'm doing wrong?
-
Mark Haney
--
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Re: File Size Script Help - Working Version
Hi Jonathan,
Argh, really stupid mistake by me. ) But let's use it to explain some
points a bit further, shall we?
A skilled craftsman knows his tools well, and Perl programmer (with CPAN as
THE collection of tools of all sizes and meanings) has an advantage here: even
if documentation is a bit vague about what's going on, we are (usually)
able to check the code itself to find the answers. )
By browsing File::Spec source (found via 'Source' link within the
'File::Spec' page at CPAN)...
http://cpansearch.perl.org/src/SMUELLER/PathTools-3.33/lib/File/Spec.pm
...we soon discover that this module is essentially an adapter for modules
like File::Spec::Unix, File::Spec::Mac, File::Spec::Win32 etc.
So our search goes on (as your mention of .DS_Store file implies) over
there:
http://cpansearch.perl.org/src/SMUELLER/PathTools-3.33/lib/File/Spec/Mac.pm
Now we may either check the documentation (which clearly states that only
the last argument to catfile is considered a filename, and all the others
will be concatenated with catdir), or look right into the code - and come
to the same conclusion:
sub catfile {
my $self = shift;
return '' unless @_;
my $file = pop @_;
return $file unless @_;
my $dir = $self-catdir(@_);
$file =~ s/^://s;
return $dir.$file;
}
So what should we do now? ) Of course, give milk to our cat... and
arguments to File::Spec's catfile! ) Like this:
File::Spec-catfile($path, $dircontents . '.md5')
... or this...
File::Spec-catfile($path, $dircontents.md5)
(check 'variable interpolation in Perl' to see why it's possible - and why
this is essentially the same as previous codeline)
... or even this ...
File::Spec-catfile($path, join '.', $dircontents, 'md5')
(but that would be a bit overkill, of course :)
Speaking of overkills: you used regex (=~ /^\./) to check whether the line
begins with a dot - or not. )
It's ok for this task, but you probably should know that these checks may
be also done with (substr($line, 0, 1) eq '.') code,
which will be a bit (up to 30% at my PC when Benchmark'ed) faster.
-- iD
2011/12/30 Jonathan Harris jtnhar...@googlemail.com
I tried to use your suggestion
open my $wr_fh, '', File::Spec-catfile($path, $dircontents, '.md5') or
die $!, $/
but it returned an error on the command line:
'Not a directory'
At which point the program dies (which is what it is supposed to do!)
I used it inside the loop - sorry to bug you for clarification
if ($dircontents=~/^\./ || -d $dircontents) {
next;
}
This is also to avoid the file .DS_Store
Re: File Size Script Help - Working Version
Hi John, yes, good point! Totally forgot this. ) Adding new files to a directory as you browse it is just not right, of course. Possible, but not right. ) I'd solve this by using hash with filenames as keys and collected 'result' strings (with md5 and filesizes) as values, filled by File::Find target routine. After the whole directory is processed, this hash should be 'written out' into the target directory. Another way to do it is to collect all the filenames instead into a list (with glob operator, for example), and process this list after. BTW (to Jonathan), I wonder do you really need to store this kind of data in different files? No offence... but I can hardly imagine how this data will be used later unless gathered into some array or hash. ) -- iD 2011/12/30 John W. Krahn jwkr...@shaw.ca Jonathan Harris wrote: Hi John Thanks for your 2 cents I hadn't considered that the module wouldn't be portable That is not what I was implying. I was saying that when you add new files to a directory that you are traversing you _may_ get irregular results. It depends on how your operating system updates directory entries.
Re: File Size Script Help - Working Version
On Fri, Dec 30, 2011 at 11:58 AM, Igor Dovgiy ivd.pri...@gmail.com wrote: Hi John, yes, good point! Totally forgot this. ) Adding new files to a directory as you browse it is just not right, of course. Possible, but not right. ) I'd solve this by using hash with filenames as keys and collected 'result' strings (with md5 and filesizes) as values, filled by File::Find target routine. After the whole directory is processed, this hash should be 'written out' into the target directory. Another way to do it is to collect all the filenames instead into a list (with glob operator, for example), and process this list after. BTW (to Jonathan), I wonder do you really need to store this kind of data in different files? No offence... but I can hardly imagine how this data will be used later unless gathered into some array or hash. ) -- iD 2011/12/30 John W. Krahn jwkr...@shaw.ca Jonathan Harris wrote: Hi John Thanks for your 2 cents I hadn't considered that the module wouldn't be portable That is not what I was implying. I was saying that when you add new files to a directory that you are traversing you _may_ get irregular results. It depends on how your operating system updates directory entries. Hi All John - Thanks for the clarification In this instance the script has been run on OSX - it seems that adding the files into the directory that is being traversed works ok this time However for best practice, I would certainly look into writing to a separate directory, and then moving the files back, as I appreciate that this fortune may not necessarily be repeated in a different environment! Igor - Firstly - File::Spec Thanks for your insight and well explained investigation - I have been learning a lot from this File::Spec has proven a most useful tool in joining and 'stringifying' the paths In the original post about this script, I had spoken about considering using a hash for the file data I'm still convinced that ultimately, this would be the way forwards I have found some scripts online concerning finding duplicate files They use md5 and/or file sizes to compare the files These are written into hashes Fully understanding some of these scripts is a little beyond my level at the moment I have attached an interesting one for you to look at (you may be aware of it already!) However, it has proved quite inspiring! (substr($line, 0, 1) eq '.') Haven't learned this yet! It looks like a good solution if it is so much more efficient - thanks for the introduction - I'll be reading up asap! BTW (to Jonathan), I wonder do you really need to store this kind of data in different files? No offence... but I can hardly imagine how this data will be used later unless gathered into some array or hash. ) There is a good reason for this! Talking to guys who work in video on demand, it seems that it is standard practice to do this for file delivery requirements As each video file must be identical upon receipt as it was upon delivery ( and that the files are all treated as unique delivery instances ) a separate accompanying file is required I thought that Perl would be a good choice for accomplishing this requirement as it is renowned for file handling # Thanks to everyone for your help and contributions - particularly Jim, Shlomi, John and Igor I have learned crazy amounts already! Happy New Year to you all! Jonathan finddupes3.plx Description: Binary data -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: What does = means?
Yes, I agree the code looks strange. Do you have any idea to do this
with a clear code? I mean to find two same letters, p in @a?
Xi
On Thu, Dec 29, 2011 at 10:17 PM, John W. Krahn jwkr...@shaw.ca wrote:
Xi Chen wrote:
Hello everyone,
I saw a code below to get two same letters p in @a.
@a = qw (D D p O H p A O);
foreach $b （@a）{
$n =~ /$b/i;
if($n= 2){
$m = $b;
}
}
But I don't know what does = mean. Thank you!
It means greater than or equal to. The expression $n = 2 is true if
the value in $n is equal to 2 or is any value greater than 2, 6 for example.
If the value in $n is less than 2 then the expression is false.
Your algorithm looks weird though because you are testing $n for the
presence of alphabetic characters (and then not using that information) and
then using $n in a numerical context.
John
--
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more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
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Re: What does = means?
Hi Xi,
You're looking only for 'p' letters, not D and O? Why?
Anyway, generic solution will be something like...
my %seen;
my @repeated = grep { /some regex here/ $seen{$_} N } @source_array;
... where N is how many times the symbols should appear in the source array
to be counted as duplicate.
and 'some regex' is, well, some regex to filter the symbols if needed. :)
-- iD
2011/12/30 Xi Chen cxde...@gmail.com
Yes, I agree the code looks strange. Do you have any idea to do this
with a clear code? I mean to find two same letters, p in @a?
Xi
On Thu, Dec 29, 2011 at 10:17 PM, John W. Krahn jwkr...@shaw.ca wrote:
Xi Chen wrote:
Hello everyone,
I saw a code below to get two same letters p in @a.
@a = qw (D D p O H p A O);
foreach $b （@a）{
$n =~ /$b/i;
if($n= 2){
$m = $b;
}
}
But I don't know what does = mean. Thank you!
It means greater than or equal to. The expression $n = 2 is true if
the value in $n is equal to 2 or is any value greater than 2, 6 for
example.
If the value in $n is less than 2 then the expression is false.
Your algorithm looks weird though because you are testing $n for the
presence of alphabetic characters (and then not using that information)
and
then using $n in a numerical context.
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
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Re: What does = means?
Oh my, of course it should be...
my @repeated = grep { /some regex here/ ++$seen{$_} N } @source_array;
... to work properly.
-- iD
2011/12/30 Igor Dovgiy ivd.pri...@gmail.com
Hi Xi,
You're looking only for 'p' letters, not D and O? Why?
Anyway, generic solution will be something like...
my %seen;
my @repeated = grep { /some regex here/ $seen{$_} N } @source_array;
... where N is how many times the symbols should appear in the source
array to be counted as duplicate.
and 'some regex' is, well, some regex to filter the symbols if needed. :)
-- iD
2011/12/30 Xi Chen cxde...@gmail.com
Yes, I agree the code looks strange. Do you have any idea to do this
with a clear code? I mean to find two same letters, p in @a?
Xi
On Thu, Dec 29, 2011 at 10:17 PM, John W. Krahn jwkr...@shaw.ca wrote:
Xi Chen wrote:
Hello everyone,
I saw a code below to get two same letters p in @a.
@a = qw (D D p O H p A O);
foreach $b （@a）{
$n =~ /$b/i;
if($n= 2){
$m = $b;
}
}
But I don't know what does = mean. Thank you!
It means greater than or equal to. The expression $n = 2 is true
if
the value in $n is equal to 2 or is any value greater than 2, 6 for
example.
If the value in $n is less than 2 then the expression is false.
Your algorithm looks weird though because you are testing $n for the
presence of alphabetic characters (and then not using that information)
and
then using $n in a numerical context.
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
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Re: What does = means?
in this code what is the
$n =~ /$b/i;
On Fri, Dec 30, 2011 at 11:53 AM, John Riselvato jdriselv...@gmail.comwrote:
in this code what is the
$n =~ /$b/i;
On Fri, Dec 30, 2011 at 10:51 AM, Igor Dovgiy ivd.pri...@gmail.comwrote:
Oh my, of course it should be...
my @repeated = grep { /some regex here/ ++$seen{$_} N }
@source_array;
... to work properly.
-- iD
2011/12/30 Igor Dovgiy ivd.pri...@gmail.com
Hi Xi,
You're looking only for 'p' letters, not D and O? Why?
Anyway, generic solution will be something like...
my %seen;
my @repeated = grep { /some regex here/ $seen{$_} N }
@source_array;
... where N is how many times the symbols should appear in the source
array to be counted as duplicate.
and 'some regex' is, well, some regex to filter the symbols if needed.
:)
-- iD
2011/12/30 Xi Chen cxde...@gmail.com
Yes, I agree the code looks strange. Do you have any idea to do this
with a clear code? I mean to find two same letters, p in @a?
Xi
On Thu, Dec 29, 2011 at 10:17 PM, John W. Krahn jwkr...@shaw.ca
wrote:
Xi Chen wrote:
Hello everyone,
I saw a code below to get two same letters p in @a.
@a = qw (D D p O H p A O);
foreach $b （@a）{
$n =~ /$b/i;
if($n= 2){
$m = $b;
}
}
But I don't know what does = mean. Thank you!
It means greater than or equal to. The expression $n = 2 is
true
if
the value in $n is equal to 2 or is any value greater than 2, 6 for
example.
If the value in $n is less than 2 then the expression is false.
Your algorithm looks weird though because you are testing $n for the
presence of alphabetic characters (and then not using that
information)
and
then using $n in a numerical context.
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
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problem with passing variables
I'm not sure if this is the right list for this, so bear with me. If it
isn't I'll be glad to post it on the correct one.
I've got a problem with passing variables to a SQL server inside a CGI
script. My code is like this:
my $begin_time = 2011-11-16 11:00:00;
my $end_time = 2011-11-16 12:00:00;
my $dbh = DBI-connect('dbi:mysql:database=embdev', 'user', 'password');
my $sql = q/SELECT * FROM events WHERE date BETWEEN $begin_time and
$end_time/;
my $sth = $dbh-prepare($sql);
$sth-execute();
I'm not sure why it's not using the the variables, can someone point out
what I'm doing wrong?
-
Mark Haney
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Review: Perl for Perl Newbies Part 5 - Good Programming Practices
Hi all, I've finally finished writing the 5th part of Perl for Perl Newbies: http://www.shlomifish.org/lecture/Perl/Newbies/lecture5/ I'd like people on this list to review it, and comment. Note that the series of presentations was also directed at absolute beginners (though I may not have been successful in it being suitable for them), and its philosophy is explained here and here: * http://www.shlomifish.org/lecture/Perl/Newbies/ * http://perl-begin.org/tutorials/#perl_for_newbies The material covered in the talks has suffered from a lot of bit rot during the many years since I've first written them, with progress in both my understanding of Perl, and in the state-of-the-art in Perl best practices, and one can refer to the books Modern Perl by chromatic and recent editions of Beginning Perl and of the Learning Perl/Intermediate Perl/Mastering Perl trio for alternatives that are possibly better. Regards, Shlomi Fish -- - Shlomi Fish http://www.shlomifish.org/ Star Trek: We, the Living Dead - http://shlom.in/st-wtld Staring at XSLT code for one minute has a 67% chance of making one permanently blind. Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: problem with passing variables
Hi Mark,
If your variables are strictly internal and by no means might be ever
tainted (read: user input), what you're doing is mostly ok.
But you need to quote the dates passed within query itself, like this:
my $sql = qq/SELECT * FROM `events` WHERE `date` BETWEEN '$begin_time' AND
'$end_time'/;
*(qq, of course, not q: you'd like your variables to be interpolated, would
you? :)*
But there's another (and in my opinion, usually better) way: using prepared
sql statement:
my $sth = $dbh-prepare(q/
SELECT * FROM `events` WHERE `date` BETWEEN ? AND ?
/);
$sth-execute($begin_time, $end_time);
This method is safer, but a little (or not, depending on driver and DB
used) bit slower than direct queries.
Have to say that I usually prefer even simpler DBI methods, like
selectall_arrayref, combining the power of `prepare`, `execute` and `fetch`
methods in one statement. But that's a matter of taste, I guess. )
-- iD
P.S. BTW, if you want to know the reason why particular SQL query fails,
just call errstr method of your DBI object (like $dbh-errstr) - and print
the result. )
2011/12/30 Mark Haney ma...@abemblem.com
I'm not sure if this is the right list for this, so bear with me. If it
isn't I'll be glad to post it on the correct one.
I've got a problem with passing variables to a SQL server inside a CGI
script. My code is like this:
my $begin_time = 2011-11-16 11:00:00;
my $end_time = 2011-11-16 12:00:00;
my $dbh = DBI-connect('dbi:mysql:**database=embdev', 'user', 'password');
my $sql = q/SELECT * FROM events WHERE date BETWEEN $begin_time and
$end_time/;
my $sth = $dbh-prepare($sql);
$sth-execute();
I'm not sure why it's not using the the variables, can someone point out
what I'm doing wrong?
-
Mark Haney
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Re: problem with passing variables
On Fri, 30 Dec 2011 12:08:50 -0500
Mark Haney ma...@abemblem.com wrote:
I'm not sure if this is the right list for this, so bear with me. If it
isn't I'll be glad to post it on the correct one.
I've got a problem with passing variables to a SQL server inside a CGI
script. My code is like this:
my $begin_time = 2011-11-16 11:00:00;
my $end_time = 2011-11-16 12:00:00;
my $dbh = DBI-connect('dbi:mysql:database=embdev', 'user', 'password');
my $sql = q/SELECT * FROM events WHERE date BETWEEN $begin_time and
$end_time/;
my $sth = $dbh-prepare($sql);
$sth-execute();
I'm not sure why it's not using the the variables, can someone point out
what I'm doing wrong?
Please use placeholders:
* http://en.wikipedia.org/wiki/SQL_injection
* http://bobby-tables.com/
The problem with your code is that Perl only expands variables inside strings
(called string-interpolation) only when these strings are notated - not later
on. The best way to solve it is using placeholders, which will also help
mitigate SQL injection problems.
Regards,
Shlomi Fish
--
-
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The Human Hacking Field Guide - http://shlom.in/hhfg
I’d love to change the world, but they won’t give me the source code.
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Re: problem with passing variables
On 12/30/2011 12:30 PM, Igor Dovgiy wrote: Hi Mark, If your variables are strictly internal and by no means might be ever tainted (read: user input), what you're doing is mostly ok. But you need to quote the dates passed within query itself, like this: my $sql = qq/SELECT * FROM `events` WHERE `date` BETWEEN '$begin_time' AND '$end_time'/; /(qq, of course, not q: you'd like your variables to be interpolated, would you? :)/ Yeah, true. I missed that part. But there's another (and in my opinion, usually better) way: using prepared sql statement: my $sth = $dbh-prepare(q/ SELECT * FROM `events` WHERE `date` BETWEEN ? AND ? /); $sth-execute($begin_time, $end_time); I can certainly do it this way, however, my ultimate goal is to have these variables passed via a web form and since I'm still getting my feet wet with using perl to a MySQL database exclusively (I can do SQL very well, but never inside perl) I am taking baby steps. This method is safer, but a little (or not, depending on driver and DB used) bit slower than direct queries. Have to say that I usually prefer even simpler DBI methods, like selectall_arrayref, combining the power of `prepare`, `execute` and `fetch` methods in one statement. But that's a matter of taste, I guess. ) -- iD P.S. BTW, if you want to know the reason why particular SQL query fails, just call errstr method of your DBI object (like $dbh-errstr) - and print the result. )
Re: problem with passing variables
Hi Mark, On Fri, 30 Dec 2011 12:39:04 -0500 Mark Haney ma...@abemblem.com wrote: On 12/30/2011 12:30 PM, Igor Dovgiy wrote: Hi Mark, If your variables are strictly internal and by no means might be ever tainted (read: user input), what you're doing is mostly ok. But you need to quote the dates passed within query itself, like this: my $sql = qq/SELECT * FROM `events` WHERE `date` BETWEEN '$begin_time' AND '$end_time'/; /(qq, of course, not q: you'd like your variables to be interpolated, would you? :)/ Yeah, true. I missed that part. But there's another (and in my opinion, usually better) way: using prepared sql statement: my $sth = $dbh-prepare(q/ SELECT * FROM `events` WHERE `date` BETWEEN ? AND ? /); $sth-execute($begin_time, $end_time); I can certainly do it this way, however, my ultimate goal is to have these variables passed via a web form and since I'm still getting my feet wet with using perl to a MySQL database exclusively (I can do SQL very well, but never inside perl) I am taking baby steps. If you're going to pass variables from a web form into Perl, then *definitely* use placeholders (unless you want an SQL injection problem on your hand). If you want something more higher-level, then you can look at Object-Relational Mappers such as http://search.cpan.org/dist/DBIx-Class/ (not necessarily the best, but the elephant in the room) or http://search.cpan.org/dist/KiokuDB/ (which is an Object-Graph storage engine), and a form handler such as http://search.cpan.org/dist/HTML-FormFu/ . Regards, Shlomi Fish -- - Shlomi Fish http://www.shlomifish.org/ What does Zionism mean? - http://shlom.in/def-zionism Chuck Norris is the greatest man in history. He killed all the great men who could ever pose a competition. Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: problem with passing variables
If you pass into SQL query something assigned by user, use placeholders by all means. ) It's not that hard, but it'll save you a lot of headaches, believe me. ) 2011/12/30 Mark Haney ma...@abemblem.com But there's another (and in my opinion, usually better) way: using prepared sql statement: my $sth = $dbh-prepare(q/ SELECT * FROM `events` WHERE `date` BETWEEN ? AND ? /); $sth-execute($begin_time, $end_time); I can certainly do it this way, however, my ultimate goal is to have these variables passed via a web form and since I'm still getting my feet wet with using perl to a MySQL database exclusively (I can do SQL very well, but never inside perl) I am taking baby steps.
What is the $_ variable?
I am confused what this variable does: $_ If someone could give an example or explanation of what this variable $_ does in perl, that would be great! Thanx. -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: File Size Script Help - Working Version
On Thu, Dec 29, 2011 at 03:43:19PM +, Jonathan Harris wrote:
Hi All
Hello Jonathan:
(Disclaimer: I stayed up all night playing Skyrim and am running
on about 4.5 hours of sleep.. ^_^)
I think most things have already been addressed, but I think Igor
might have had a bit of trouble making it clear.
opendir (my $in, $path) or die Cannot open $dir: $!\n;
find (\wanted, $path);
close $in;
opendir (my $totalin, $path) or die Cannot open $dir: $!\n;
find (\cleanup, $path);
close $totalin;
AFAICT, it's completely nonsensical to open a directory file
handle surrounding File::Find::find. I tried to /search the
perldoc (just in case there's some kind of magical optimization
or something) and saw no mention of 'opendir' or 'handle' (except
for the special _ file handle created for stat, lstat, etc..). So
it seems $in and $totalin are completely unnecessary here:
File::Find will worry about opening and processing the
directories for you.
sub wanted {
while ($dircontents = readdir($in)) {
I guess this is why you are opening directory handles above, but
it doesn't really make sense. You're basically only using
File::Find to loop at this point, and very obscurely. :)
File::Find's role in life is precisely to find you all the files
within a directory tree. You're reinventing the square wheel with
your use of opendir and readdir. :)
The wanted subroutine is typically used to either process the
file system tree outright, or store applicable files in data
structures for later processing. E.g.,
use strict;
use warnings;
use File::Find;
my @files;
sub wanted
{
# Skip dot files and directories.
return if substr($_, 0, 1) eq '.' || -d $_;
# If current file is a normal file, push into array for
# later.
push @files, $File::Find::name if -f $_;
}
my $path = '.';
find \wanted, $path;
# Now @files should be filled with a recursive list of files to
# process. E.g.,
for my $file (@files)
{
my $md5name = $file.'md5';
# Etc...
}
my $hex = Digest::MD5-new-addfile($fh)-hex digest;
I assume you meant `hexdigest' here, not 'hex digest'.
$newname =~ s/\ //;
Ideally if you're going to do something as obscure as this, you
should comment it in both places so future readers and
maintainers understand why it's done, even if they only read one
half of the program.
I think Igor else has already explained how to eliminate this
obscurity though. :)
Regards,
--
Brandon McCaig bamcc...@gmail.com bamcc...@castopulence.org
Castopulence Software https://www.castopulence.org/
Blog http://www.bamccaig.com/
perl -E '$_=q{V zrna gur orfg jvgu jung V fnl. }.
q{Vg qbrfa'\''g nyjnlf fbhaq gung jnl.};
tr/A-Ma-mN-Zn-z/N-Zn-zA-Ma-m/;say'
signature.asc
Description: Digital signature
Re: What is the $_ variable?
Hello Harry, On Fri, 30 Dec 2011 10:03:30 -0800 (PST) Harry kaichow...@gmail.com wrote: I am confused what this variable does: $_ If someone could give an example or explanation of what this variable $_ does in perl, that would be great! $_ is the default variable, which gets assigned to and used in various contexts. You can think of it as the pronoun it in English. Personally, I feel that overusing $_ is not recommended in most serious programs, because it is easily devastated, but: 1. You sometimes need to use it, like in http://perldoc.perl.org/functions/map.html , http://perldoc.perl.org/functions/grep.html , as well as some other functions from List::Util , List::MoreUtils , List::UtilsBy and similar modules (and even then, it is sometimes useful to assign it to a lexical my variable.). 2. It is sometimes useful in one-off programs and scripts, especially perl -pe/perl -ne/perl -pale/perl -lane/etc. scripts (where people also allow for omitting use strict; and use warnings;. Regards, Shlomi Fish -- - Shlomi Fish http://www.shlomifish.org/ My Public Domain Photos - http://www.flickr.com/photos/shlomif/ Larry Wall gets the colon. Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: problem with passing variables
On 12/30/2011 12:50 PM, Igor Dovgiy wrote: If you pass into SQL query something assigned by user, use placeholders by all means. ) It's not that hard, but it'll save you a lot of headaches, believe me. ) 2011/12/30 Mark Haney ma...@abemblem.com mailto:ma...@abemblem.com But there's another (and in my opinion, usually better) way: using prepared sql statement: my $sth = $dbh-prepare(q/ SELECT * FROM `events` WHERE `date` BETWEEN ? AND ? /); $sth-execute($begin_time, $end_time); I can certainly do it this way, however, my ultimate goal is to have these variables passed via a web form and since I'm still getting my feet wet with using perl to a MySQL database exclusively (I can do SQL very well, but never inside perl) I am taking baby steps. I'm definitely going to do it that way, now that I've had a chance to read the replies and do some more googling on the subject. My biggest issue now is parsing the form data from STDIN from a POST in a HTML form. (Which is a whole other issue and not one I'm going to address in this reply. Thanks for all the replies. They were all very helpful.
Re: problem with passing variables
Hi Mark, On Fri, 30 Dec 2011 14:19:04 -0500 Mark Haney ma...@abemblem.com wrote: On 12/30/2011 12:50 PM, Igor Dovgiy wrote: If you pass into SQL query something assigned by user, use placeholders by all means. ) It's not that hard, but it'll save you a lot of headaches, believe me. ) 2011/12/30 Mark Haney ma...@abemblem.com mailto:ma...@abemblem.com But there's another (and in my opinion, usually better) way: using prepared sql statement: my $sth = $dbh-prepare(q/ SELECT * FROM `events` WHERE `date` BETWEEN ? AND ? /); $sth-execute($begin_time, $end_time); I can certainly do it this way, however, my ultimate goal is to have these variables passed via a web form and since I'm still getting my feet wet with using perl to a MySQL database exclusively (I can do SQL very well, but never inside perl) I am taking baby steps. I'm definitely going to do it that way, now that I've had a chance to read the replies and do some more googling on the subject. I'm glad you will. My biggest issue now is parsing the form data from STDIN from a POST in a HTML form. (Which is a whole other issue and not one I'm going to address in this reply. For this you should use http://plackperl.org/ or at the very least the CGI.pm module from the Perl core (also available on CPAN - it's dual-life.), or one of its CPAN alternatives. Doing it by hand is error-prone, and not recommended. Regards, Shlomi Fish -- - Shlomi Fish http://www.shlomifish.org/ My Aphorisms - http://www.shlomifish.org/humour.html Microsoft — making it all make sense. Ours. Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: File Size Script Help - Working Version
On Fri, Dec 30, 2011 at 7:11 PM, Brandon McCaig bamcc...@gmail.com wrote:
On Thu, Dec 29, 2011 at 03:43:19PM +, Jonathan Harris wrote:
Hi All
Hello Jonathan:
(Disclaimer: I stayed up all night playing Skyrim and am running
on about 4.5 hours of sleep.. ^_^)
I think most things have already been addressed, but I think Igor
might have had a bit of trouble making it clear.
opendir (my $in, $path) or die Cannot open $dir: $!\n;
find (\wanted, $path);
close $in;
opendir (my $totalin, $path) or die Cannot open $dir: $!\n;
find (\cleanup, $path);
close $totalin;
AFAICT, it's completely nonsensical to open a directory file
handle surrounding File::Find::find. I tried to /search the
perldoc (just in case there's some kind of magical optimization
or something) and saw no mention of 'opendir' or 'handle' (except
for the special _ file handle created for stat, lstat, etc..). So
it seems $in and $totalin are completely unnecessary here:
File::Find will worry about opening and processing the
directories for you.
sub wanted {
while ($dircontents = readdir($in)) {
I guess this is why you are opening directory handles above, but
it doesn't really make sense. You're basically only using
File::Find to loop at this point, and very obscurely. :)
File::Find's role in life is precisely to find you all the files
within a directory tree. You're reinventing the square wheel with
your use of opendir and readdir. :)
The wanted subroutine is typically used to either process the
file system tree outright, or store applicable files in data
structures for later processing. E.g.,
use strict;
use warnings;
use File::Find;
my @files;
sub wanted
{
# Skip dot files and directories.
return if substr($_, 0, 1) eq '.' || -d $_;
# If current file is a normal file, push into array for
# later.
push @files, $File::Find::name if -f $_;
}
my $path = '.';
find \wanted, $path;
# Now @files should be filled with a recursive list of files to
# process. E.g.,
for my $file (@files)
{
my $md5name = $file.'md5';
# Etc...
}
my $hex = Digest::MD5-new-addfile($fh)-hex digest;
I assume you meant `hexdigest' here, not 'hex digest'.
$newname =~ s/\ //;
Ideally if you're going to do something as obscure as this, you
should comment it in both places so future readers and
maintainers understand why it's done, even if they only read one
half of the program.
I think Igor else has already explained how to eliminate this
obscurity though. :)
Regards,
--
Brandon McCaig bamcc...@gmail.com bamcc...@castopulence.org
Castopulence Software https://www.castopulence.org/
Blog http://www.bamccaig.com/
perl -E '$_=q{V zrna gur orfg jvgu jung V fnl. }.
q{Vg qbrfa'\''g nyjnlf fbhaq gung jnl.};
tr/A-Ma-mN-Zn-z/N-Zn-zA-Ma-m/;say'
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HI Brandon
Thanks for your response
I totally agree with your first point
Having now used File::Find a little more, I have seen that using opendir
was totally unneccessary and have removed them from the script
And guess what.it works fine without them!
I think that my initial confusion arose from fundamentally misunderstanding
File::Find - thinking that it required a handle, not just a path.
I have also now exchanged the while loop with a foreach loop - much better!
I assume you meant `hexdigest' here, not 'hex digest'.
You assume correctly! Gmail has started to do annoying auto text complete -
I must turn it off!!
push @files, $File::Find::name if -f $_;
This is nice and clean
Your approach is different to what we have been discussing
You seem to gather the files with File::Find and then leave that sub alone
asap
The processing is then done in the results of that gathering
My script left the processing within sub wanted
This could possible be a reason that complications arose so quickly
To get file names and sizes at the same time, I am also considering
my %files;
sub wanted {
my $filesize = (stat($_))[7];
push @{$files{$filesize}}, $File::Find::name;
}
find(\wanted, $path);
to hash files and file size results together - then process after
And yep, Igor
Re: File Size Script Help - Working Version
Great work, Jonathan!
Notice how simple your script has become - and that's a good sign as well
in Perl. :) We can make it even simpler, however.
As you probably know, Perl has two fundamental types of collections: arrays
(where data is stored as a sequence of elements, data chunks) and hashes
(where data chunks are unordered, but stored with some unique key used to
retrieve it). Sometimes hashes are used just to sort out (non-)unique data,
but that's another story.
Now look at this line:
push @{$files{$filesize}}, $File::Find::name;
Don't you see something... weird? You're using hash where filesizes are the
keys - and because, yes, they may well be non-unique, you have to store
arrays of filenames in your hash instead...
But much more natural (at least, for me) is to organize your hash (let's
call it %filedata) so that filenames (which are unique by their nature)
become the keys. And some info about these files - sizes and md5-hashes -
become the values.
For example, our `wanted` (btw, its name is misleading a bit, no? may be
'process' will sound better?) sub may look as follows:
find(\wanted, $path);
my %filedata;
sub wanted {
return if substr($_, 0, 1) eq '.' || -d $_;
my $filesize = -s _;
open my $fh, '', $_ or die $!, $/;
my $filemd5 = Digest::MD5-new-addfile($fh)-hexdigest;
close $fh;
$filedata{$_} = [$filesize, $filemd5];
}
(*Notice how you don't have to declare the global filedata hash before the
callback function is called in `find`? It's really interesting topic*)
Then you'll just have to iterate over the %filedata - and it's as easy as
writing...
for my $filename (keys %filedata) {
my ($size, $md5) = @{ $filedata{$filename} };
open my $fh, '', File::Spec-catfile($path, $filename.md5)
or die $!, $/;
print $fh $filename\t$size bytes\t$md5\n;
close $fh;
}
... yep, that easy. )
-- iD
P.S. Ordering the output should be an easy task for you; hint - look up
'sort' documentation - or just use sort system routine. :)
2011/12/31 Jonathan Harris jtnhar...@googlemail.com
HI Brandon
Thanks for your response
I totally agree with your first point
Having now used File::Find a little more, I have seen that using opendir
was totally unneccessary and have removed them from the script
And guess what.it works fine without them!
I think that my initial confusion arose from fundamentally misunderstanding
File::Find - thinking that it required a handle, not just a path.
I have also now exchanged the while loop with a foreach loop - much better!
I assume you meant `hexdigest' here, not 'hex digest'.
You assume correctly! Gmail has started to do annoying auto text complete -
I must turn it off!!
push @files, $File::Find::name if -f $_;
This is nice and clean
Your approach is different to what we have been discussing
You seem to gather the files with File::Find and then leave that sub alone
asap
The processing is then done in the results of that gathering
My script left the processing within sub wanted
This could possible be a reason that complications arose so quickly
To get file names and sizes at the same time, I am also considering
my %files;
sub wanted {
my $filesize = (stat($_))[7];
push @{$files{$filesize}}, $File::Find::name;
}
find(\wanted, $path);
to hash files and file size results together - then process after
And yep, Igor has been thorough and very helpful
Thanks again for your input on this - hope you manage to get some sleep!
All the best
Jonathan
Re: File Size Script Help - Working Version
Igor Dovgiy wrote:
Great work, Jonathan!
Notice how simple your script has become - and that's a good sign as well
in Perl. :) We can make it even simpler, however.
As you probably know, Perl has two fundamental types of collections: arrays
(where data is stored as a sequence of elements, data chunks) and hashes
(where data chunks are unordered, but stored with some unique key used to
retrieve it). Sometimes hashes are used just to sort out (non-)unique data,
but that's another story.
Now look at this line:
push @{$files{$filesize}}, $File::Find::name;
Don't you see something... weird? You're using hash where filesizes are the
keys - and because, yes, they may well be non-unique, you have to store
arrays of filenames in your hash instead...
But much more natural (at least, for me) is to organize your hash (let's
call it %filedata) so that filenames (which are unique by their nature)
become the keys. And some info about these files - sizes and md5-hashes -
become the values.
Yes, file names in a given directory _have_ to be unique, however...
For example, our `wanted` (btw, its name is misleading a bit, no? may be
'process' will sound better?) sub may look as follows:
find(\wanted, $path);
my %filedata;
sub wanted {
return if substr($_, 0, 1) eq '.' || -d $_;
my $filesize = -s _;
open my $fh, '', $_ or die $!, $/;
my $filemd5 = Digest::MD5-new-addfile($fh)-hexdigest;
close $fh;
$filedata{$_} = [$filesize, $filemd5];
You are traversing a directory tree, so using $_ as the key may cause
collisions across different directories. Better to use
$File::Find::name which contains the full absolute path name.
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
--
To unsubscribe, e-mail: beginners-unsubscr...@perl.org
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