RE: Split and concatenation
Thanks guys for your suggestion
-Original Message-
From: Shlomi Fish [mailto:shlo...@shlomifish.org]
Sent: Saturday, December 17, 2011 2:48 PM
To: vishnu.kuma...@wipro.com
Cc: beginners@perl.org
Subject: Re: Split and concatenation
Hi Vishnu,
On Sat, 17 Dec 2011 08:22:31 +
vishnu.kuma...@wipro.com wrote:
Hi,
I am trying to convert the string abc.def.ghi.amm to abcdefghiamm using split
and concatenation. I am missing something somewhere.. please help me to fix
the code
my $string = abc.def.ghi.amm;
my @d = split(/\./,$string);
No need for double-quotes around the string:
my @d = split(/\./, $string);
my $e = @d;
for (my $i=0; $i $e; $i++) {
This is better written as «for my $i (0 .. $#d)».
print(Value of array element $i is $d[$i]\n); }
#concatenation
for (my $i=0; $i $e; $i++) {
my $abc .= $d[$i];
}
print(Value after concatenation is $abc\n);
1. You should declare $abc outside the loop and concatenate to it.
2. No need for double quotes around $d[$i].
3. You can just use http://perldoc.perl.org/functions/join.html .
So your program becomes:
my $abc = join('', split(/\./, $string);
In this case it can also be written using:
my $abc = $string;
$abc =~ s/\.//g;
Or:
my $abc = $string;
$abc =~ tr/.//d;
Regards,
Shlomi Fish
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Re: Split and concatenation
On Sat, Dec 17, 2011 at 08:22:31AM +, vishnu.kuma...@wipro.com wrote:
Hi,
Hello:
I am trying to convert the string abc.def.ghi.amm to
abcdefghiamm using split and concatenation. I am missing
something somewhere.. please help me to fix the code
my $string = abc.def.ghi.amm;
my @d = split(/\./,$string);
my $e = @d;
for (my $i=0; $i $e; $i++) {
print(Value of array element $i is $d[$i]\n); }
#concatenation
for (my $i=0; $i $e; $i++) {
my $abc .= $d[$i];
}
print(Value after concatenation is $abc\n);
Output I am getting is Value after concatenation is amm
Make sure you always use the 'strict' and 'warnings' pragmas.
They should usually be the first couple of lines in every Perl
script or module file you write (i.e., right after your shebang).
use strict;
use warnings;
It looks like $abc in the file scope is not declared, and $abc
within the for-loop is only visible within that loop. That
explains your erroneous results. The 'strict' pragma would have
made it an error to refer to $abc without declaring it.
For example, executing your program with the strict and warnings
pragmas yields the following output:
Global symbol $abc requires explicit package name at - line 13.
Execution of - aborted due to compilation errors.
(Line 13 being your last line with the print statement on it)
See how Perl detects the problem for you and refuses to execute
until you fix it? Never write Perl code without these pragmas. :)
They will save you a lot of trouble.
That said, as somebody else pointed out, $abc would be undef in
your print statement (if allowed to execute i.e., without the
strict 'vars' pragma enabled) so your alleged output doesn't make
sense given what you have shown us.
The others have already shown you better ways to do this so I
guess I won't repeat them.
Please do not print this email unless it is absolutely
necessary.
/me prints this E-mail unnecessarily. :)
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Re: slicing array references
On 12/18/2011 08:53 PM, David Christensen wrote:
beginners@perl.org:
I'm working on some classes with attributes that are array and hash
references, and am confused by what happens when I attempt to slice an
array or hash reference. For example:
7. $ra-[0, 1, 2] evaluates to $ra-[2].
8. $ra-[0 .. 2] produces two Use of uninitialized value in range (or
flip) warnings and evaluates to $ra-[1].
you are missing a very important point in those two line. $ra-[] always
accesses a single element of the array (same for a hash access). so it
provides scalar context to the inside of the []. 0,1,2 in scalar context
is 2 (right value of the , operator). i would be surprised not to see a
warning of values in a void context or similar as the 0,1 are tossed
away. the 0 .. 2 is just the scalar .. (flip flop op) inside the [].
integers in that op are compares to $. (current line number from a file
being read). since there is no file i/o here $. is unefined which does
== to 0 so the boolean result of the .. op is 1. this is a very
misguided way to get 1 from that.
so remember, never use a list (or looking like a list) thing inside
$ar-[] as it is always not what you expect. it is a scalar op in all cases.
I see similar results with functions that return array references:
30. fra-[0, 1, 2]
31. fra-[0 .. 2]
no reason to be different. the issue is what is inside the [] and not
how the ref got there.
And object methods:
42. $oa-ra-[0, 1, 2]
43. $oa-ra-[0, 1, 2]
same issues.
there is no need to try variations on how the ref got there. it is
wasted coding and testing. your issue is knowing how to properly use
-[] with a ref.
as for slicing, it is actually a different story altogether and fairly
easy. the perldoc perldata covers it some. this article i wrote a long
time ago covers it in depth: http://sysarch.com/Perl/hash_slice.txt
the rule is actually very simple. the basic rule for dereferencing
applies. you can replace any name of a aggregate by a ref inside {} (i
always use {} here). so a normal slice on an array is @foo{@keys} and
the same on a ref is just @{$foo}{@keys}. done. no muss no fuss.
as i said it is much cleaner and clearer to wrap the ref in {} whenever
you do a full dereference (the - just accesses a single value and
doesn't count here).
similarly, when you just want a single item from an aggregate reference,
always use the - notation. it is much cleaner than this form:
$$ref{$key} # nasty to read
${$ref}{$key} # this is slightly better
$ref-{$key} # this is best by far
so in conclusion,
slicing is not super common but can save some coding when used right. it
makes no difference where the ref comes from. slicing always puts the []
or {} in list context. accessing a single element is best done with
$ref- notation and it always puts the inside of []/{} in scalar
context. slices are meant for a list of accesses (read OR write) and -
is meant for a single access.
uri
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re: File Size Script Help
Hi Perl Pros
This is my first call for help
I am a totally new, self teaching, Perl hopeful
If my approach to this script is simply wrong, please let me know as it
will help my learning!
The script aims to:
1) Read in a directory either from the command line, or from a default path
2) Produce a hash for future checksum
3) Write this (hex digest) to a separate file, in a sub directory of the
parent, which has the same name and a .md5 extension
4) Check the original file for its size
5) Add this data to the newly created file on a new line (in bytes)
I have a script that will do most of this, except for analysing the file
size - I think that the file size being analysed may be the md5 object
result as the same value is printed to each file
I am running out of ideas and would appreciate any help you could give!
I have tried using File::stat::OO and File::stat - but to no avail - I
could be using them incorrectly!
Many thanks in advance...
Jon.
Here are some details:
System:
Mac OSX 10.7.2
Perl version 5.12
Script:
#!/usr/bin/perl
# md5-test-3.plx
use warnings;
use strict;
use Digest::MD5;
my $filesize = 0;
my $dir = shift || '/Users/jonharris/Documents/begperl';
opendir (DH, $dir) or die Couldn't open directory: $!;
my $md5 = Digest::MD5-new;
while ($_ = readdir(DH)) {
$md5-add($_);
$filesize = (stat(DH))[7];
Is it necessary to put the following into a new loop?
foreach ($_) {
open FH, /Users/jonharris/Documents/begperl/md5/$_.md5 or die $!;
binmode(FH);
print FH $md5-hexdigest, \n, $filesize;
}
close FH;
}
close DH;
print \n$dir\n\n;
###
Re: File Size Script Help
On 12/19/11 Mon Dec 19, 2011 11:32 AM, Jonathan Harris
jtnhar...@googlemail.com scribbled:
Hi Perl Pros
This is my first call for help
I am a totally new, self teaching, Perl hopeful
If my approach to this script is simply wrong, please let me know as it
will help my learning!
The script aims to:
1) Read in a directory either from the command line, or from a default path
2) Produce a hash for future checksum
A hash of what? File names (directory contents) or file contents?
3) Write this (hex digest) to a separate file, in a sub directory of the
parent, which has the same name and a .md5 extension
Same name as the file or same name as the directory?
4) Check the original file for its size
5) Add this data to the newly created file on a new line (in bytes)
Will this file contain information for one file or many files?
I have a script that will do most of this, except for analysing the file
size - I think that the file size being analysed may be the md5 object
result as the same value is printed to each file
Print out the file size returned by stat. Check if it is the same displayed
by the ls command.
I am running out of ideas and would appreciate any help you could give!
I have tried using File::stat::OO and File::stat - but to no avail - I
could be using them incorrectly!
I am afraid I do not understand exactly what you are trying to accomplish. I
can't tell from your program whether or not you will end up with one digest
file for the entire directory, or one digest file for each file in the
directory.
Many thanks in advance...
Jon.
Here are some details:
System:
Mac OSX 10.7.2
Perl version 5.12
Script:
#!/usr/bin/perl
# md5-test-3.plx
use warnings;
use strict;
use Digest::MD5;
my $filesize = 0;
You should declare variables where they are needed and not before.
my $dir = shift || '/Users/jonharris/Documents/begperl';
opendir (DH, $dir) or die Couldn't open directory: $!;
my $md5 = Digest::MD5-new;
while ($_ = readdir(DH)) {
You are better off using a scalar variable and not the default variable,
which can get reused and overwritten:
while( my $file = readdir(DH) ) {
$md5-add($_);
You are adding file names to a string to be digested. Is that what you
want? Or do you want to calculate a digest for the contents of each file?
I have not used Digest::MD5, but if you to calculate the digest for the
contents of each file, you want to create a new digest object, open the
file, and use the addfile() method, then hexdigest() for each file.
$filesize = (stat(DH))[7];
You are applying stat to the directory read handle. You want to fetch data
for the file (untested):
my $filesize = (stat($dir/$file))[7];
Note that you must prefix the file name with its full path.
Is it necessary to put the following into a new loop?
No. It makes no sense to have a one-iteration loop.
foreach ($_) {
open FH, /Users/jonharris/Documents/begperl/md5/$_.md5 or die $!;
You are appending lines to a file with a name that is based on an existing
file. Why?
binmode(FH);
There is no need to set the mode of the output file to binary. Both
hexdigest and the file size will be written in ascii characters, not binary
data.
print FH $md5-hexdigest, \n, $filesize;
}
close FH;
}
close DH;
print \n$dir\n\n;
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Re: File Size Script Help
Hi Jonathan,
some comments on your code - both positive and negative.
On Mon, 19 Dec 2011 19:32:10 +
Jonathan Harris jtnhar...@googlemail.com wrote:
Hi Perl Pros
This is my first call for help
I am a totally new, self teaching, Perl hopeful
If my approach to this script is simply wrong, please let me know as it
will help my learning!
The script aims to:
1) Read in a directory either from the command line, or from a default path
2) Produce a hash for future checksum
3) Write this (hex digest) to a separate file, in a sub directory of the
parent, which has the same name and a .md5 extension
4) Check the original file for its size
5) Add this data to the newly created file on a new line (in bytes)
I have a script that will do most of this, except for analysing the file
size - I think that the file size being analysed may be the md5 object
result as the same value is printed to each file
I am running out of ideas and would appreciate any help you could give!
I have tried using File::stat::OO and File::stat - but to no avail - I
could be using them incorrectly!
Many thanks in advance...
Jon.
Here are some details:
System:
Mac OSX 10.7.2
Perl version 5.12
Script:
#!/usr/bin/perl
# md5-test-3.plx
use warnings;
use strict;
strict and warnings are good.
use Digest::MD5;
So is using a module.
my $filesize = 0;
You shouldn't predeclare your variables.
my $dir = shift || '/Users/jonharris/Documents/begperl';
opendir (DH, $dir) or die Couldn't open directory: $!;
Don't use bareword dir handles - use lexical ones. It's good that you're using
the or die thing, though.
my $md5 = Digest::MD5-new;
Seems like you're using the same $md5 object times and again which will
calculate cumulative MD5 sums instead of per-file ones.
while ($_ = readdir(DH)) {
1. You're not skipping . and ...
2. You're not skipping other directories.
3. The $_ variable can be easily devastated. You should use a lexical one.
$md5-add($_);
According to http://metacpan.org/module/Digest::MD5 the add() methods adds
data, and here it will only add the filename. You need to use addfile() with an
opened file handle instead.
$filesize = (stat(DH))[7];
You shouldn't stat the directory handle. Instead stat $dir/$filename (you can
also use the core File::Spec module if you want to make it extra portable).
Is it necessary to put the following into a new loop?
foreach ($_) {
Why the foreach ($_) here? It does nothing. You're already iterating on the
files.
open FH, /Users/jonharris/Documents/begperl/md5/$_.md5 or die $!;
binmode(FH);
print FH $md5-hexdigest, \n, $filesize;
}
close FH;
Use lexical file handles here, use three-args open - «open my $fh, '',
'/Users'» and don't open it time and again. Keep it outside the loop.
For more information see:
http://perl-begin.org/tutorials/bad-elements/
Regards,
Shlomi Fish
}
close DH;
print \n$dir\n\n;
###
--
-
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Chuck Norris/etc. Facts - http://www.shlomifish.org/humour/bits/facts/
We don’t know his cellphone number, and even if we did, we would tell you that
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Re: File Size Script Help
On Mon, Dec 19, 2011 at 8:08 PM, Jim Gibson jimsgib...@gmail.com wrote:
On 12/19/11 Mon Dec 19, 2011 11:32 AM, Jonathan Harris
jtnhar...@googlemail.com scribbled:
Hi Perl Pros
This is my first call for help
I am a totally new, self teaching, Perl hopeful
If my approach to this script is simply wrong, please let me know as it
will help my learning!
The script aims to:
1) Read in a directory either from the command line, or from a default
path
2) Produce a hash for future checksum
A hash of what? File names (directory contents) or file contents?
3) Write this (hex digest) to a separate file, in a sub directory of the
parent, which has the same name and a .md5 extension
Same name as the file or same name as the directory?
4) Check the original file for its size
5) Add this data to the newly created file on a new line (in bytes)
Will this file contain information for one file or many files?
I have a script that will do most of this, except for analysing the file
size - I think that the file size being analysed may be the md5 object
result as the same value is printed to each file
Print out the file size returned by stat. Check if it is the same displayed
by the ls command.
I am running out of ideas and would appreciate any help you could give!
I have tried using File::stat::OO and File::stat - but to no avail - I
could be using them incorrectly!
I am afraid I do not understand exactly what you are trying to accomplish.
I
can't tell from your program whether or not you will end up with one digest
file for the entire directory, or one digest file for each file in the
directory.
Many thanks in advance...
Jon.
Here are some details:
System:
Mac OSX 10.7.2
Perl version 5.12
Script:
#!/usr/bin/perl
# md5-test-3.plx
use warnings;
use strict;
use Digest::MD5;
my $filesize = 0;
You should declare variables where they are needed and not before.
my $dir = shift || '/Users/jonharris/Documents/begperl';
opendir (DH, $dir) or die Couldn't open directory: $!;
my $md5 = Digest::MD5-new;
while ($_ = readdir(DH)) {
You are better off using a scalar variable and not the default variable,
which can get reused and overwritten:
while( my $file = readdir(DH) ) {
$md5-add($_);
You are adding file names to a string to be digested. Is that what you
want? Or do you want to calculate a digest for the contents of each file?
I have not used Digest::MD5, but if you to calculate the digest for the
contents of each file, you want to create a new digest object, open the
file, and use the addfile() method, then hexdigest() for each file.
$filesize = (stat(DH))[7];
You are applying stat to the directory read handle. You want to fetch data
for the file (untested):
my $filesize = (stat($dir/$file))[7];
Note that you must prefix the file name with its full path.
Is it necessary to put the following into a new loop?
No. It makes no sense to have a one-iteration loop.
foreach ($_) {
open FH, /Users/jonharris/Documents/begperl/md5/$_.md5 or die $!;
You are appending lines to a file with a name that is based on an existing
file. Why?
binmode(FH);
There is no need to set the mode of the output file to binary. Both
hexdigest and the file size will be written in ascii characters, not binary
data.
print FH $md5-hexdigest, \n, $filesize;
}
close FH;
}
close DH;
print \n$dir\n\n;
###
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Hi Jim
Thanks for responding
Here are some answers to your questions:
A hash of what? File names (directory contents) or file contents?
The aim is to produce a digest for each file in the folder
Same name as the file or same name as the directory?
Each file created will have the same filename as the original, but with the
extension '.md5'
Will this file contain information for one file or many files?
This file will contain information for only one file
This is so that when looking at the treated directory, the end result will
be:
some_movie.mov
some_movie.mov.md5
another_movie.mov
another_movie.mov.md5
etc...
Print out the file size returned by stat. Check if it is the same
displayed
by the ls command.
I really have! However, this is where I am coming unstuck
I am afraid I do not understand exactly what you are trying to
accomplish. I
can't tell from your program whether or not you will end up with one
digest
file for the entire directory, or one digest file for each file in the
directory.
The program creates one digest file for each file in the directory : )
my $filesize = 0;
You should declare variables where they are needed and not before.
Noted
my $md5 = Digest::MD5-new;
while ($_ = readdir(DH)) {
You are better off using a scalar variable and not the default variable,
Re: File Size Script Help
On Mon, Dec 19, 2011 at 8:09 PM, Shlomi Fish shlo...@shlomifish.org wrote:
Hi Jonathan,
some comments on your code - both positive and negative.
On Mon, 19 Dec 2011 19:32:10 +
Jonathan Harris jtnhar...@googlemail.com wrote:
Hi Perl Pros
This is my first call for help
I am a totally new, self teaching, Perl hopeful
If my approach to this script is simply wrong, please let me know as it
will help my learning!
The script aims to:
1) Read in a directory either from the command line, or from a default
path
2) Produce a hash for future checksum
3) Write this (hex digest) to a separate file, in a sub directory of the
parent, which has the same name and a .md5 extension
4) Check the original file for its size
5) Add this data to the newly created file on a new line (in bytes)
I have a script that will do most of this, except for analysing the file
size - I think that the file size being analysed may be the md5 object
result as the same value is printed to each file
I am running out of ideas and would appreciate any help you could give!
I have tried using File::stat::OO and File::stat - but to no avail - I
could be using them incorrectly!
Many thanks in advance...
Jon.
Here are some details:
System:
Mac OSX 10.7.2
Perl version 5.12
Script:
#!/usr/bin/perl
# md5-test-3.plx
use warnings;
use strict;
strict and warnings are good.
use Digest::MD5;
So is using a module.
my $filesize = 0;
You shouldn't predeclare your variables.
my $dir = shift || '/Users/jonharris/Documents/begperl';
opendir (DH, $dir) or die Couldn't open directory: $!;
Don't use bareword dir handles - use lexical ones. It's good that you're
using
the or die thing, though.
my $md5 = Digest::MD5-new;
Seems like you're using the same $md5 object times and again which will
calculate cumulative MD5 sums instead of per-file ones.
while ($_ = readdir(DH)) {
1. You're not skipping . and ...
2. You're not skipping other directories.
3. The $_ variable can be easily devastated. You should use a lexical one.
$md5-add($_);
According to http://metacpan.org/module/Digest::MD5 the add() methods
adds
data, and here it will only add the filename. You need to use addfile()
with an
opened file handle instead.
$filesize = (stat(DH))[7];
You shouldn't stat the directory handle. Instead stat $dir/$filename
(you can
also use the core File::Spec module if you want to make it extra portable).
Is it necessary to put the following into a new loop?
foreach ($_) {
Why the foreach ($_) here? It does nothing. You're already iterating on the
files.
open FH, /Users/jonharris/Documents/begperl/md5/$_.md5 or die $!;
binmode(FH);
print FH $md5-hexdigest, \n, $filesize;
}
close FH;
Use lexical file handles here, use three-args open - «open my $fh, '',
'/Users'» and don't open it time and again. Keep it outside the loop.
For more information see:
http://perl-begin.org/tutorials/bad-elements/
Regards,
Shlomi Fish
}
close DH;
print \n$dir\n\n;
###
--
-
Shlomi Fish http://www.shlomifish.org/
Chuck Norris/etc. Facts - http://www.shlomifish.org/humour/bits/facts/
We don’t know his cellphone number, and even if we did, we would tell you
that
we didn’t know it.
Please reply to list if it's a mailing list post - http://shlom.in/reply .
Hi Shlomi
Thanks for your response
To answer your questions:
my $filesize = 0;
You shouldn't predeclare your variables
Noted, thanks
my $dir = shift || '/Users/jonharris/Documents/begperl';
opendir (DH, $dir) or die Couldn't open directory: $!;
Don't use bareword dir handles - use lexical ones. It's good that you're
using
the or die thing, though.
Of course - will have to re-read the section on barewords...
my $md5 = Digest::MD5-new;
Seems like you're using the same $md5 object times and again which will
calculate cumulative MD5 sums instead of per-file ones.
In which case, I think that it will have to go in the loop so that a new
instance is produced each time?
while ($_ = readdir(DH)) {
1. You're not skipping . and ...
2. You're not skipping other directories.
I'm sure I read somewhere, that the parent was automatically skipped
Must be getting confused
However, adding this will be ok:
next if $_ eq . or $_ eq ..;
3. The $_ variable can be easily devastated. You should use a lexical one.
I'll certainly use lexical in the future
$md5-add($_);
According to http://metacpan.org/module/Digest::MD5 the add() methods
adds
data, and here it will only add the filename. You need to use addfile()
with an
opened file handle instead.
That makes sense
$filesize = (stat(DH))[7];
You shouldn't stat the directory handle. Instead stat $dir/$filename
(you can
also use the core File::Spec module if you want to make
