[31261] in Perl-Users-Digest
Perl-Users Digest, Issue: 2506 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Mon Jul 6 18:14:24 2009
Date: Mon, 6 Jul 2009 15:14:16 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Mon, 6 Jul 2009 Volume: 11 Number: 2506
Today's topics:
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings <smallpond@juno.com>
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings <ben@morrow.me.uk>
Re: Perl scalars as numbers or character strings <smallpond@juno.com>
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings <uri@stemsystems.com>
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings <uri@stemsystems.com>
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings <tadmc@seesig.invalid>
Re: Perl scalars as numbers or character strings <paul@peschoen.com>
Re: Perl scalars as numbers or character strings <jurgenex@hotmail.com>
Re: Perl scalars as numbers or character strings sln@netherlands.com
Re: Perl scalars as numbers or character strings <tadmc@seesig.invalid>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Mon, 06 Jul 2009 13:12:27 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <a1m4555k437ib6eiellfjuio94hd5q8hng@4ax.com>
On Mon, 06 Jul 2009 19:52:52 GMT, "Paul E. Schoen" <paul@peschoen.com> wrote:
>I am trying to understand scalar variables, and I found the following:
>http://www.tutorialspoint.com/perl/perl_scalars.htm
>
>Here is an excerpt:
WARNING!!! You do not have strick/warnings turned on!
>
> #!/usr/bin/perl
>
> $number = "5";
> $exponent = "2 ** 8";
> $string = "Hello, PERL!";
> $float = 12.39;
>
> # We can also assign a scalar an empty (undefined) value:
> $nothing = undef;
>
> # Printing all the above values
> print "$number\n";
> print "$exponent\n";
> print "$string\n";
> print "$float\n";
> print "There is nothing: $nothing\n";
Warning, undefined value in print!
>
> This will give following result
> 5
> 2 ** 8
> Hello, PERL!
> 12.39
> There is nothing:
>
>My question is whether $number, $exponent, and $float are actually numbers
>or character strings,
No and Yes. But if you continue to try to confuse yourself by naming the
variables what you think they contain, you've already lost the war on the
understanding of Perl.
> particularly those that are enclosed in quotes. Thus,
>what would be the result of:
>
> $mynum = $number * $float;
> print "$mynum";
> print $mynum;
> $mynum = 2 ** 8;
> print "$mynum"
>
>And what happens if you add characters and variables in a print statement?
>
> print "This is a number$mynum2";
>
The context of the variable as used in the print statement at the time it is
parsed will be used.
>The information in the FAQ did not seem to address this except as follows:
>
> my $string = '0644';
>
> print $string + 0; # prints 644
>
> print $string + 44; # prints 688, certainly not octal!
if ($string * 1 == 644) {
print "string + 44 = ", $string + 44, "\n";
}
>
>It seems like the printf and sprintf functions work as I would expect,
>
> printf "0%o %d", $number, $number;
>
>But what happens if you use the following:
>
> $number = "0123";
> $number = "A123";
> $number = "one";
> $number = 123;
> $number = 123 + 4.56;
> $number = "123 + 4.56";
> $number = "123" + "4.56";
>
>Sorry for the noobish questions, but I am used to C and Delphi Pascal,
>where I am familiar with the syntax.
>
>Thanks,
>
>Paul
>
Its all how you use it. Use it as a string, its a string. Number, a number.
It appears Perl uses a few representations of the same variable, it appears.
-sln
------------------------------
Date: Mon, 06 Jul 2009 16:16:43 -0400
From: Steve C <smallpond@juno.com>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <h2tmbm$cuc$1@news.eternal-september.org>
Paul E. Schoen wrote:
>
> My question is whether $number, $exponent, and $float are actually numbers
> or character strings, particularly those that are enclosed in quotes. Thus,
> what would be the result of:
What do you mean by "actually"?
perl -e '$num=5; $str="5"; print "actually" if $num == $str'
actually
>
> Sorry for the noobish questions, but I am used to C and Delphi Pascal,
> where I am familiar with the syntax.
>
You can't learn perl from a C manual. Be that as it may, in C I can do:
double d;
d = 5; /* Wait! I thought 5 was an integer! What's going on? */
perl is like C with a much smarter compiler.
------------------------------
Date: Mon, 06 Jul 2009 13:27:01 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <1en4555b9a295de48iknltsvmuqb9dsbt1@4ax.com>
On Mon, 06 Jul 2009 16:16:43 -0400, Steve C <smallpond@juno.com> wrote:
>Paul E. Schoen wrote:
>>
>> My question is whether $number, $exponent, and $float are actually numbers
>> or character strings, particularly those that are enclosed in quotes. Thus,
>> what would be the result of:
>
>What do you mean by "actually"?
>perl -e '$num=5; $str="5"; print "actually" if $num == $str'
>actually
>
>>
>> Sorry for the noobish questions, but I am used to C and Delphi Pascal,
>> where I am familiar with the syntax.
>>
>
>You can't learn perl from a C manual. Be that as it may, in C I can do:
>
>double d;
>d = 5; /* Wait! I thought 5 was an integer! What's going on? */
>
>perl is like C with a much smarter compiler.
Not exactly, Perl is like C, with a structural variant representation
of values per variable.
-sln
------------------------------
Date: Mon, 6 Jul 2009 21:21:30 +0100
From: Ben Morrow <ben@morrow.me.uk>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <av2ai6-m3m2.ln1@osiris.mauzo.dyndns.org>
Quoth "Paul E. Schoen" <paul@peschoen.com>:
> I am trying to understand scalar variables, and I found the following:
> http://www.tutorialspoint.com/perl/perl_scalars.htm
>
> Here is an excerpt:
>
> #!/usr/bin/perl
>
> $number = "5";
> $exponent = "2 ** 8";
> $string = "Hello, PERL!";
> $float = 12.39;
>
> # We can also assign a scalar an empty (undefined) value:
> $nothing = undef;
<snip>
>
> My question is whether $number, $exponent, and $float are actually numbers
> or character strings, particularly those that are enclosed in quotes.
$number, $exponent and $string are (currently) strings. $float is a
(floating-point) number. However, Perl will auto-convert string<->number
(and int<->float) whenever it becomes necessary.
> Thus,
> what would be the result of:
<snip>
>
> And what happens if you add characters and variables in a print statement?
<snip>
What happened when you tried it?
> Sorry for the noobish questions, but I am used to C and Delphi Pascal,
> where I am familiar with the syntax.
I think you need to stop reading random web tutorials and read an actual
beginners' book on Perl. I would normally recommend reading the docs
rather than a book, but it looks like you are someone who would benefit
from a more structured approach than the docs provide. The FAQ has
several (good) recommendations, under perldoc -q book.
Ben
------------------------------
Date: Mon, 06 Jul 2009 16:47:47 -0400
From: Steve C <smallpond@juno.com>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <h2to5t$p5k$1@news.eternal-september.org>
sln@netherlands.com wrote:
> On Mon, 06 Jul 2009 16:16:43 -0400, Steve C <smallpond@juno.com> wrote:
>
>> Paul E. Schoen wrote:
>>> My question is whether $number, $exponent, and $float are actually numbers
>>> or character strings, particularly those that are enclosed in quotes. Thus,
>>> what would be the result of:
>> What do you mean by "actually"?
>> perl -e '$num=5; $str="5"; print "actually" if $num == $str'
>> actually
>>
>>> Sorry for the noobish questions, but I am used to C and Delphi Pascal,
>>> where I am familiar with the syntax.
>>>
>> You can't learn perl from a C manual. Be that as it may, in C I can do:
>>
>> double d;
>> d = 5; /* Wait! I thought 5 was an integer! What's going on? */
>>
>> perl is like C with a much smarter compiler.
>
> Not exactly, Perl is like C, with a structural variant representation
> of values per variable.
>
> -sln
unions are structural variant variables in C.
------------------------------
Date: Mon, 06 Jul 2009 14:00:25 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <6mo4559n3bcc3b06go7a12rlail4bfjurp@4ax.com>
On Mon, 06 Jul 2009 13:12:27 -0700, sln@netherlands.com wrote:
>On Mon, 06 Jul 2009 19:52:52 GMT, "Paul E. Schoen" <paul@peschoen.com> wrote:
>
>>I am trying to understand scalar variables, and I found the following:
>>http://www.tutorialspoint.com/perl/perl_scalars.htm
>>
As a simple example, a Perl variable is a C structure containing
types (a union if you will), where the particular code usage is
determined at parstime (and will vary in different parts of the code),
and determined at runtime (mostly).
So like:
var variable {
char *;
int;
float;
...
}
If the particular spot in the code is used as a string,
it will use char *. If that is empty, it will grab int or float
and convert it to char *, assign it to char * (in the structure)
and use it dynamically at run time.
The same goes for all the other variants. In this regard its no
different than any typless language, say like JScript. There are rules
and defaults as always, as it percolates up to the parser and runtime
engine.
-sln
------------------------------
Date: Mon, 06 Jul 2009 14:04:00 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <jkp455937caqoiii6qabb0nehqmh2ev21b@4ax.com>
On Mon, 06 Jul 2009 16:47:47 -0400, Steve C <smallpond@juno.com> wrote:
>sln@netherlands.com wrote:
>> On Mon, 06 Jul 2009 16:16:43 -0400, Steve C <smallpond@juno.com> wrote:
>>
>>> Paul E. Schoen wrote:
>>>> My question is whether $number, $exponent, and $float are actually numbers
>>>> or character strings, particularly those that are enclosed in quotes. Thus,
>>>> what would be the result of:
>>> What do you mean by "actually"?
>>> perl -e '$num=5; $str="5"; print "actually" if $num == $str'
>>> actually
>>>
>>>> Sorry for the noobish questions, but I am used to C and Delphi Pascal,
>>>> where I am familiar with the syntax.
>>>>
>>> You can't learn perl from a C manual. Be that as it may, in C I can do:
>>>
>>> double d;
>>> d = 5; /* Wait! I thought 5 was an integer! What's going on? */
>>>
>>> perl is like C with a much smarter compiler.
>>
>> Not exactly, Perl is like C, with a structural variant representation
>> of values per variable.
>>
>> -sln
>
>unions are structural variant variables in C.
You can only be as dumb as the language you use.
-sln
------------------------------
Date: Mon, 06 Jul 2009 17:05:02 -0400
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <87zlbh1q0x.fsf@quad.sysarch.com>
>>>>> "PES" == Paul E Schoen <paul@peschoen.com> writes:
as for you, how you are learning perl is bizarre given your claim to
know c and other langs. do you know shell at all? awk even? unix in
general? perl is best understood as being born of that environment
(including c) and stealing the best of breeds from each.
PES> I am trying to understand scalar variables, and I found the following:
PES> http://www.tutorialspoint.com/perl/perl_scalars.htm
yeah! i haven't done this in a while and i am in the mood for it. i have
found extremely few perl tutorials on the net worth a single bit of
space. i have done reviews (google for them) and i need to vent some on
this one.
i moved this to the top so you can read my summary.
i have to stop now. of course i can go on. there is lots here and some
of it is useful but as typical there is poor writing and too many
mistakes, misconceptions, inaccuracies. what is needed for all those web
tutes on perl is a good editor. they never seem to be written by someone
active in the perl community as they would have gotten useful feedback
that way. given the free beginning perl book and perl's own great
documentation (including many tutorials now) why these web tutes still
are found is beyond me.
uri
from the scalars page:
$number = "5";
that is a string, not a number
$exponent = "2 ** 8";
$string = "Hello, PERL!";
$float = 12.39;
# We can also assign a scalar an empty (undefined) value:
$nothing = undef;
it prints:
There is nothing:
the empty string is more appropriate as it won't trigger a warning.
from the page on arrays:
@10 = (1 .. 10);
@100 = (1 .. 100;
@1000 = (100 .. 1000);
using numbers for var names works but is dumb as hell.
@abc = (a .. z);
the last one will warn on unquoted strings
print "@10"; # Prints number starting from 1 to 10
print "@100"; # Prints number starting from 1 to 100
print "@1000"; # Prints number starting from 1 to 1000
the comment should be from 100. and do you want to print 900 numbers on
one line for a demo?
print "@abc"; # Prints number starting from a to z
that is not a number.
When adding elements using push() or shift() you must specify
two arguments, first the array name and second the name of the
element to add.
wrong. push and unshift take a list of elements to add to the array. and
you don't pass in the array name but the array variable. and what is the
'name of the element to add'? how would i push 1 as it has no name? or
an anon reference which has no name?
from the Object Oriented section:
Within Perl, an object is merely a reference to a data type that
knows what class it belongs to. The object is stored as a
reference in a scalar variable. Because a scalar only contains a
reference to the object, the same scalar can hold different
objects in different classes.
that is sara palin logic! what about a hash element holding an object?
what does different classes have to do with a single reference? it is
just the ability of a scalar value to be a reference to a blessed object
that is the core of perl's object flexibility.
Perl provides a bless() function which is used to return a
reference and which becomes an object.
bless associates a perl datum to a class. it is passed in a reference to
that datum and returns it. it does not create the reference which is
what the above statement implies.
the list of topics has this whopper!
Perl Error Handeling
how does he handle that error? :)
from the Perl IF..ELSE.. section (sic)
The final conditional statement is actually an operator.the
conditional operator. It is synonymous with the if...else
conditional statement but is shorter and more compact. The
format for the operator is:
(expression) ? (statement if true) : (statement if false)
huh? those are expressions, not statements. teaching that is the way to
get nasty precedence issues with ?:.
For example, we can emulate the previous example as follows:
($date == $today) ? print "Happy B.Day!\n" : print "Happy Day!\n";
and he doesn't even obey the previous style as () were not used. it will
work here because : is low binding but if you put an assignment in there
it breaks without the parens. also it subverts the purpose of ?: which
is to return a value based on a condition, not to do side effects. that
would better be written as:
print ($date == $today) ? "Happy B.Day!\n" : "Happy Day!\n";
which removes the redundant print calls, is shorter and proper.
from the operators page (edited a bit):
There are many Perl operators but here are a few of the most
common ones:
Arithmetic Operators
+ addition
- subtraction
* multiplication
/ division
Numeric Comparison Operators
== equality
!= inequality
String Comparison Operators
le less than or equal
ge greater than or equal
the comparison ops are the most common ops? who uses ge and le often?? i
can't recall the last time i actually used those!!
the only other text on this page is a copy of the precedence
table. that's it. basic math, comparison ops and then precedence with
nothing on any other ops.
from the regular expressions page:
There are three regular expression operators within Perl
* Match Regular Expression - m//
* Substitute Regular Expression - s///
* Transliterate Regular Expression - tr///
this is a classic tutorial laugher, calling tr/// a regex op.
the rest of this page has minimal explanations of regexes but a table of
all the modifiers. it shows $1 being used but with no explanation. there
is a minimal cheat sheet on character classes, anchors, etc.
it covers ?PATTERN? which is rarely used and newbies will not want to
learn about it. it is used mostly in more complex parsers and such to
match only one time.
so you could read perlretut and perlrequick and learn more from better
and more accurate writing.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.sysarch.com --
----- Perl Code Review , Architecture, Development, Training, Support ------
--------- Free Perl Training --- http://perlhunter.com/college.html ---------
--------- Gourmet Hot Cocoa Mix ---- http://bestfriendscocoa.com ---------
------------------------------
Date: Mon, 06 Jul 2009 14:08:03 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <bqp455dovuvnp0ime3rh932bfeq87v9ju2@4ax.com>
On Mon, 06 Jul 2009 17:05:02 -0400, Uri Guttman <uri@stemsystems.com> wrote:
>>>>>> "PES" == Paul E Schoen <paul@peschoen.com> writes:
>
>as for you, how you are learning perl is bizarre given your claim to
>know c and other langs. do you know shell at all? awk even? unix in
>general? perl is best understood as being born of that environment
>(including c) and stealing the best of breeds from each.
Whats your claim, apparently you know everything, sort of a jack-off
of all trades.
-sln
------------------------------
Date: Mon, 06 Jul 2009 17:10:07 -0400
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <87r5wt1psg.fsf@quad.sysarch.com>
>>>>> "s" == sln <sln@netherlands.com> writes:
s> On Mon, 06 Jul 2009 17:05:02 -0400, Uri Guttman <uri@stemsystems.com> wrote:
>>>>>>> "PES" == Paul E Schoen <paul@peschoen.com> writes:
>>
>> as for you, how you are learning perl is bizarre given your claim to
>> know c and other langs. do you know shell at all? awk even? unix in
>> general? perl is best understood as being born of that environment
>> (including c) and stealing the best of breeds from each.
s> Whats your claim, apparently you know everything, sort of a jack-off
s> of all trades.
i know enough to not help you get a perl job. that is all i need to
know.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.sysarch.com --
----- Perl Code Review , Architecture, Development, Training, Support ------
--------- Free Perl Training --- http://perlhunter.com/college.html ---------
--------- Gourmet Hot Cocoa Mix ---- http://bestfriendscocoa.com ---------
------------------------------
Date: Mon, 06 Jul 2009 14:11:58 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <a3q4555l1gc00191u4f6v6toina1a80l13@4ax.com>
On Mon, 06 Jul 2009 17:10:07 -0400, Uri Guttman <uri@stemsystems.com> wrote:
>>>>>> "s" == sln <sln@netherlands.com> writes:
>
> s> On Mon, 06 Jul 2009 17:05:02 -0400, Uri Guttman <uri@stemsystems.com> wrote:
> >>>>>>> "PES" == Paul E Schoen <paul@peschoen.com> writes:
> >>
> >> as for you, how you are learning perl is bizarre given your claim to
> >> know c and other langs. do you know shell at all? awk even? unix in
> >> general? perl is best understood as being born of that environment
> >> (including c) and stealing the best of breeds from each.
>
> s> Whats your claim, apparently you know everything, sort of a jack-off
> s> of all trades.
>
>i know enough to not help you get a perl job. that is all i need to
>know.
>
>uri
I work for Google as a Perl manager. Don't let your resume pass my desk!
-sln
------------------------------
Date: Mon, 06 Jul 2009 16:37:56 -0500
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <slrnh54re1.ccf.tadmc@tadmc30.sbcglobal.net>
sln@netherlands.com <sln@netherlands.com> wrote:
> I work for Google as a Perl manager.
Pffft!
Daydreaming of having a position is not actually the
same as having acquired that position...
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Mon, 06 Jul 2009 21:49:08 GMT
From: "Paul E. Schoen" <paul@peschoen.com>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <oju4m.1185$P5.277@nwrddc02.gnilink.net>
"Uri Guttman" <uri@stemsystems.com> wrote in message
news:87zlbh1q0x.fsf@quad.sysarch.com...
>>>>>> "PES" == Paul E Schoen <paul@peschoen.com> writes:
>
> as for you, how you are learning perl is bizarre given your claim to
> know c and other langs. do you know shell at all? awk even? unix in
> general? perl is best understood as being born of that environment
> (including c) and stealing the best of breeds from each.
I think I have a general aversion to languages that make assumptions about
variables, and that includes JavaScript and VB. I know enough C and Delphi
to make fairly complex Windows GUI applications that operate on a nearly
real-time basis with serial communication and data analysis, and I use a
version of C for some PIC projects, but mostly I use assembly.
I don't know shell. I found this:
http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html
I have seen awk programs. I am not familiar with the syntax.
I know a few unix commands and I have used FTP and Telnet, but that's about
it. It seems similar to MSDOS but with more powerful features (like grep).
> PES> I am trying to understand scalar variables, and I found the
> following:
> PES> http://www.tutorialspoint.com/perl/perl_scalars.htm
>
> yeah! i haven't done this in a while and i am in the mood for it. i have
> found extremely few perl tutorials on the net worth a single bit of
> space. i have done reviews (google for them) and i need to vent some on
> this one.
Thanks for the warnings about on-line tutorials and other sources of
information. Even I found an error where a /E should have been \E:
$PARTIALCAPS = "\UThis half will/E become capital!";
I think it will not be worth it for me to learn enough Perl to do even the
simple things I may want to do. I should probably just hire an expert or
use some canned scripts and web apps, and stick with what I know.
Paul
------------------------------
Date: Mon, 06 Jul 2009 14:52:13 -0700
From: Jürgen Exner <jurgenex@hotmail.com>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <f4r455l2jin42dm42oau1643c8caaqu1kc@4ax.com>
"Paul E. Schoen" <paul@peschoen.com> wrote:
>I am trying to understand scalar variables, and I found the following:
>http://www.tutorialspoint.com/perl/perl_scalars.htm
>
>Here is an excerpt:
>
> #!/usr/bin/perl
>
> $number = "5";
> $exponent = "2 ** 8";
> $string = "Hello, PERL!";
> $float = 12.39;
>
> # We can also assign a scalar an empty (undefined) value:
> $nothing = undef;
>
> # Printing all the above values
> print "$number\n";
> print "$exponent\n";
> print "$string\n";
> print "$float\n";
> print "There is nothing: $nothing\n";
>
> This will give following result
> 5
> 2 ** 8
> Hello, PERL!
> 12.39
> There is nothing:
>
>My question is whether $number, $exponent, and $float are actually numbers
>or character strings, particularly those that are enclosed in quotes.
First two are strings (exactly because they are enclosed in quotes),
$float is a number.
BUT(!!!): in Perl any string also has a numerical value and any number
also has a string value (and a boolean value, too).
>Thus,
>what would be the result of:
>
> $mynum = $number * $float;
Perl recognizes that $number, although a string, is used as a number and
therefore takes its numerical value, which happens to be 5.
If you had
$mynum = $exponent * $float;
then the numerical value of the string "2 ** 8" wold be 2, not 256!
> print "$mynum";
This is a useless use of quotes. See "perldoc -q always":
What's wrong with always quoting "$vars"?
> print $mynum;
> $mynum = 2 ** 8;
> print "$mynum"
Same here
>And what happens if you add characters and variables in a print statement?
>
> print "This is a number$mynum2";
You are using the variable $mynum2 instead of the variable $mynum.
If you want to print another character directly after the value of the
variable then enclose the variable name in curly brackets:
print "This is a number${mynum}2";
>The information in the FAQ did not seem to address this except as follows:
>
> my $string = '0644';
> print $string + 0; # prints 644
> print $string + 44; # prints 688, certainly not octal!
Totally different issue, that's about numbers with leading 0s, which
normally are interpreted as octal, but not so when explicitely marked as
strings by enclosing them in quotes.
>But what happens if you use the following:
>
> $number = "0123";
Numerical value is 123.
> $number = "A123";
Numerical value is 0 (and when used in numerical context you will also
get a warning about "argument not numerical").
> $number = "one";
Numerical value is 0 (and when used in numerical context you will also
get a warning about "argument not numerical").
> $number = 123;
Numerical value is 123.
> $number = 123 + 4.56;
Numerical value is 127.56.
> $number = "123 + 4.56";
Numerical value is 123 and when used in numerical context you will also
get a warning about "argument not numerical".
> $number = "123" + "4.56";
The + operator creates numerical context, thus you are adding the
numerical values of the strings "123" and "4.56", which happen to be 123
and 4.56, thus $number contains 127.56.
jue
------------------------------
Date: Mon, 06 Jul 2009 14:57:29 -0700
From: sln@netherlands.com
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <mos455tvc1mmft2r3ltim1d7nj254fmfhs@4ax.com>
On Mon, 06 Jul 2009 21:49:08 GMT, "Paul E. Schoen" <paul@peschoen.com> wrote:
>
>"Uri Guttman" <uri@stemsystems.com> wrote in message
>news:87zlbh1q0x.fsf@quad.sysarch.com...
>>>>>>> "PES" == Paul E Schoen <paul@peschoen.com> writes:
>>
>> as for you, how you are learning perl is bizarre given your claim to
>> know c and other langs. do you know shell at all? awk even? unix in
>> general? perl is best understood as being born of that environment
>> (including c) and stealing the best of breeds from each.
>
>I think I have a general aversion to languages that make assumptions about
>variables, and that includes JavaScript and VB. I know enough C and Delphi
>to make fairly complex Windows GUI applications that operate on a nearly
>real-time basis with serial communication and data analysis, and I use a
>version of C for some PIC projects, but mostly I use assembly.
>
>I don't know shell. I found this:
>http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html
>
>I have seen awk programs. I am not familiar with the syntax.
>
>I know a few unix commands and I have used FTP and Telnet, but that's about
>it. It seems similar to MSDOS but with more powerful features (like grep).
>
>
>> PES> I am trying to understand scalar variables, and I found the
>> following:
>> PES> http://www.tutorialspoint.com/perl/perl_scalars.htm
>>
>> yeah! i haven't done this in a while and i am in the mood for it. i have
>> found extremely few perl tutorials on the net worth a single bit of
>> space. i have done reviews (google for them) and i need to vent some on
>> this one.
>
>Thanks for the warnings about on-line tutorials and other sources of
>information. Even I found an error where a /E should have been \E:
>
> $PARTIALCAPS = "\UThis half will/E become capital!";
>
>I think it will not be worth it for me to learn enough Perl to do even the
>simple things I may want to do. I should probably just hire an expert or
>use some canned scripts and web apps, and stick with what I know.
>
>Paul
>
Even though I have a job, I would do some side contract work for you.
-sln
------------------------------
Date: Mon, 06 Jul 2009 16:59:00 -0500
From: Tad J McClellan <tadmc@seesig.invalid>
Subject: Re: Perl scalars as numbers or character strings
Message-Id: <slrnh54slh.ccf.tadmc@tadmc30.sbcglobal.net>
Paul E. Schoen <paul@peschoen.com> wrote:
> I am trying to understand scalar variables, and I found the following:
[ snip URL of a random tutorial found on "the web" ]
You will save yourself a lot of pain if you stop using your
current approach to learning this stuff.
Searching the web for "tutorial" type of information will almost
always lead to crap that will confuse rather than enlighten you.
There are precious few "good" tutorials out there, and as a beginner
you won't be able to tell the (few) good ones from the (many) bad ones.
You will save a boatload of time and pain if you learn it "right"
the first time...
... you should probably consider buying or borrowing a tutorial
book rather than letting web crap pollute your mental model.
Don't just go to the bookstore and pick a book either, there are
more than a few crappy Perl books out there too.
Do a bit of research to find a book that has a good reputation
among people who DO know Perl.
perldoc -q book
will suggest several.
Or, you could at least start with one that is most surely non-crap:
http://www.perl.org/books/beginning-perl/
> Here is an excerpt:
No thanks, I watch the Colbert Report when I want laughs.
I've no time to laugh at the foolishness embodied in the
random thingie that you've stumbled upon.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
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