Re: file test doesn't seem to be working
>>> "Brett W. McCoy" <[EMAIL PROTECTED]> 2/5/2002 10:35:48 AM >>> > >That's just more a matter of style -- I get the willies when subroutines >modify global values invisibly. Great advice. thanks -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: file test doesn't seem to be working
On Tue, 5 Feb 2002, John Mooney wrote:
> Actually, it is not an incorrect way I believe, so much as he is using
> slightly incorrect syntax. From the Nutshell ...
I really meant 'incorrect' in its usage, not the syntax -- he was using it
in a void context.
> ... I think the key is that he was not using a token that resulted in an
> explicit evaluation, returning & capturing a result. By wrapping the 2nd
> and 3rd tokens of the ternary clause in parens, this result can be
> acheived.
>
> Here's an example I use often in CGIs to accomplish background-color
> swapping in HTML table rows - achieiving an old computer-paper,
> green/white effect:
>
> local $swapper = -1; # globals
> local $bgcolor = '';
>
> sub swapBGcolor {
>(($swapper *= -1) > 0 ) ? ($bgcolor="#FF") : ($bgcolor="#F5DCC7");
> }
That can be dangerous, IMHO, modifying globals like that (I know it would
cause some problems in mod_perl!) I would instead code it so that the
little subroutine returns the value you need:
$bgcolor = swapBGcolor();
sub swapBGcolor {
return ($swapper *= -1) > 0 ? '#FF' : '#F5DCC7'
}
That's just more a matter of style -- I get the willies when subroutines
modify global values invisibly.
-- Brett
http://www.chapelperilous.net/
The English have no respect for their language, and will not teach
their children to speak it.
-- G. B. Shaw
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Re: file test doesn't seem to be working
>>> "Brett W. McCoy" <[EMAIL PROTECTED]> 2/4/2002 9:28:42 PM >>>
>>On Mon, 4 Feb 2002, david wright wrote:
>>
>> i can't use the ternary operator like this? (damn waste if not) thanks.
>>
>> foreach $dup (@array){
>> (-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
>> )
>
>Yes, that is an incorrect way to use the ?: operator -- the operataor is
>handed an expression that yields a boolean value, and it returns a value
>based on what that boolean value is:
>
> Here is a one liner that accomplishes what you want:
>
>$ perl -e '$ans = (-d "/usr/bin") ? "yes\n" : "no\n"; print $ans'
>yes
>
Actually, it is not an incorrect way I believe, so much as he is using slightly
incorrect syntax. From the Nutshell ...
Ternary ?: is the conditional operator. It works much like an if-then-else statement,
but it can safely be embedded within other operations and functions.
test_expr ? if_true_expr : if_false_expr
If the test_expr is true, only the if_true_expr is evaluated. Otherwise, only the
if_false_expr is evaluated. Either way, the value of the _evaluated_expression_
becomes the value of the entire expression.
I think the key is that he was not using a token that resulted in an explicit
evaluation, returning & capturing a result. By wrapping the 2nd and 3rd tokens of the
ternary clause in parens, this result can be acheived.
Here's an example I use often in CGIs to accomplish background-color swapping in HTML
table rows - achieiving an old computer-paper, green/white effect:
local $swapper = -1; # globals
local $bgcolor = '';
sub swapBGcolor {
(($swapper *= -1) > 0 ) ? ($bgcolor="#FF") : ($bgcolor="#F5DCC7");
}
Each time swapBGcolor is invoked, the value of $swapper is multiplied by -1, flipping
between +1 or -1. When that var is positive, the TRUE expression of the ternary
opertaor is 'evaluated', assigning a value to $bgcolor at the same time. When $swapper
is negative (false), the 2nd value of the global $bgcolor is assigned during the
'evaluation'.
I remember struggling with getting this to work and finally hitting upon using parens
to capture the result of an expression and returning it to the ? operator's result.
FYI
- John
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Re: file test doesn't seem to be working
On Feb 4, Brett W. McCoy said:
>On Mon, 4 Feb 2002, david wright wrote:
>
>> i can't use the ternary operator like this? (damn waste if not) thanks.
>>
>> foreach $dup (@array){
>> (-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
>> )
>
>Yes, that is an incorrect way to use the ?: operator -- the operataor is
>handed an expression that yields a boolean value, and it returns a value
>based on what that boolean value is:
That's not to say his use is incorrect.
EXPR ? EXPR : EXPR
His code fits...
(-d $dup) ? (print "yes: $dup\n") : (print "no: $dup\n")
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
** Look for "Regular Expressions in Perl" published by Manning, in 2002 **
what does y/// stand for? why, yansliterate of course.
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Re: file test doesn't seem to be working
On Mon, 4 Feb 2002, david wright wrote:
> i can't use the ternary operator like this? (damn waste if not) thanks.
>
> foreach $dup (@array){
> (-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
> )
Yes, that is an incorrect way to use the ?: operator -- the operataor is
handed an expression that yields a boolean value, and it returns a value
based on what that boolean value is:
Here is a one liner that accomplishes what you want:
$ perl -e '$ans = (-d "/usr/bin") ? "yes\n" : "no\n"; print $ans'
yes
-- Brett
http://www.chapelperilous.net/
"The Lord gave us farmers two strong hands so we could grab as much as
we could with both of them."
-- Joseph Heller, "Catch-22"
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Re: file test doesn't seem to be working
David Wright wrote:
>
> i am sending @array a directory (i.e. example /usr/dw5) which contains a
> lot of files and folders (directories).
> (i have already checked the value of @array and $dup and they are as
> desired.) What i want to accomplish is: print yes, "$dup (file name)" if
> it's a directory (folder) i am testing it on a directory which is
> composed of 90% folders. The example below will only print yes for .
> and .. and "no" for everything else. I have tried it with other file
> test's (i.e. -f, -A, -e, etc,...) none of them work as desired,... maybe
> i can't use the ternary operator like this? (damn waste if not) thanks.
>
> foreach $dup (@array){
> (-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
> )
This works fine on my Linux system. BTW this is usually written as:
print -d $dup ? 'yes: ' : 'no: ', "$dup\n";
John
--
use Perl;
program
fulfillment
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Re: file test doesn't seem to be working
On Monday, February 4, 2002, at 07:26 PM, Jeff 'japhy' Pinyan wrote:
> On Feb 4, david wright said:
>
>> i am sending @array a directory (i.e. example /usr/dw5) which
>> contains a
>> lot of files and folders (directories).
>
> Be warned that readdir() returns NAMES, not PATHS.
>
> opendir DIR, "/some/dir";
> @files = readdir DIR;
> closedir DIR;
>
> @files will contain (".", "..", "file1", "blah", ...). Notice how those
> names do NOT have "/some/dir/" at the beginning?
>
> for (@files) {
> print "$_ is ok\n" if -d "/some/dir/$_";
> }
>
> --
> Jeff "japhy" Pinyan [EMAIL PROTECTED]
> http://www.pobox.com/~japhy/
> RPI Acacia brother #734 http://www.perlmonks.org/
> http://www.cpan.org/
> ** Look for "Regular Expressions in Perl" published by Manning, in
> 2002 **
> what does y/// stand for? why, yansliterate of
> course.
>
>
Damn it, now it makes sense, exactly,... it's just reading a "string" it
doesn't know what it's representing, that's why i have to chdir.
(Guess that answers my question of my i would have to chdir if i can
readdir ;-) ) excellent!
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Re: file test doesn't seem to be working
On Feb 4, david wright said:
>i am sending @array a directory (i.e. example /usr/dw5) which contains a
>lot of files and folders (directories).
Be warned that readdir() returns NAMES, not PATHS.
opendir DIR, "/some/dir";
@files = readdir DIR;
closedir DIR;
@files will contain (".", "..", "file1", "blah", ...). Notice how those
names do NOT have "/some/dir/" at the beginning?
for (@files) {
print "$_ is ok\n" if -d "/some/dir/$_";
}
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
RPI Acacia brother #734 http://www.perlmonks.org/ http://www.cpan.org/
** Look for "Regular Expressions in Perl" published by Manning, in 2002 **
what does y/// stand for? why, yansliterate of course.
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Re: file test doesn't seem to be working
On Monday, February 4, 2002, at 06:57 PM, Timothy Johnson wrote:
>
> Did you chdir to the directory? Otherwise your script might be
> checking the
> wrong directory.
>
> opendir(DIR,"/mydir");
> @array = readdir(DIR);
> chdir "/mydir";
> foreach $dup (@array){
> (-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
> }
>
>
well the return value of @array prints all the files in the desired
directory, doesn't that mean that is the directory that the loop is
operating on and -d is checking?
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RE: file test doesn't seem to be working
Did you chdir to the directory? Otherwise your script might be checking the
wrong directory.
opendir(DIR,"/mydir");
@array = readdir(DIR);
chdir "/mydir";
foreach $dup (@array){
(-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
}
-Original Message-
From: david wright [mailto:[EMAIL PROTECTED]]
Sent: Monday, February 04, 2002 5:51 PM
To: [EMAIL PROTECTED]
Subject: file test doesn't seem to be working
i am sending @array a directory (i.e. example /usr/dw5) which contains a
lot of files and folders (directories).
(i have already checked the value of @array and $dup and they are as
desired.) What i want to accomplish is: print yes, "$dup (file name)" if
it's a directory (folder) i am testing it on a directory which is
composed of 90% folders. The example below will only print yes for .
and .. and "no" for everything else. I have tried it with other file
test's (i.e. -f, -A, -e, etc,...) none of them work as desired,... maybe
i can't use the ternary operator like this? (damn waste if not) thanks.
foreach $dup (@array){
(-d $dup) ? print "yes: $dup \n": print "no: $dup \n";
)
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