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Can I iterate through a file on a CGI page?
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Subject Author Date
Can I iterate through a file on a CGI page? Rich Grise 04-01-2008
Posted by Rich Grise on April 1, 2008, 9:05 pm
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 Apologies to Perl purists - comp.infosystems.www.authoring.cgi doesn't
work on my newsreader, and this is a CGI question:

What I want to do is, I've got a large collection of image files:
$ wc gallery-pix
37448 62619 3218967 gallery-pix

and what I'd like to do is look at each of the 37488 image files on
some kind of page, with buttons like "Keep", "Skip", and "Quit",
so I can page through all of these images, which are strewn all
over the Samba server, and decide which ones might look good on
the website.

So, is it possible to do something like (in pseudocode):

for each $line in <file> {
show webpage with <img> tag, and the three buttons;
get button response, decide what to do with file;
if button == "Quit", save place in source file;
next;

or so?

Thanks,
Rich



Posted by David Filmer on April 1, 2008, 9:41 pm
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 Rich Grise wrote:
> for each $line in <file> {

This is gonna be your problem. CGI is stateless. Each time you hit one
of the submit buttons you will re-invoke the program, and the new
invocation knows nothing about the state of the previous invocation. If
you attempted something like you wrote then you would keep showing the
first item over and over again, because it would start at the beginning
of the file each time you invoked the program.

There are several things you can do to get around this issue. My
preference is to use a database instead of a file, and run my CGI under
a mod_perl webserver which is smart enough to cache the database handle.
But maybe that's overkill for what you want to do.

If you are willing to pay the price of opening up your flatfile each
time you invoke the program, you could pass the current (or next) line
number as a hidden() parameter. Thus the program knows which line of
the file to process next (I would recommend tying the file to an array
so the line number simply becomes the array subscript).




Posted by xhoster on April 2, 2008, 12:07 am
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> Apologies to Perl purists - comp.infosystems.www.authoring.cgi doesn't
> work on my newsreader, and this is a CGI question:
>
> What I want to do is, I've got a large collection of image files:
> $ wc gallery-pix
> 37448 62619 3218967 gallery-pix
>
> and what I'd like to do is look at each of the 37488 image files on
> some kind of page, with buttons like "Keep", "Skip", and "Quit",
> so I can page through all of these images, which are strewn all
> over the Samba server, and decide which ones might look good on
> the website.
>
> So, is it possible to do something like (in pseudocode):
>
> for each $line in <file> {

In CGI, your program won't survive for the loop to iterate. Unless
you are making one page with all 37448 files on it.

> show webpage with <img> tag, and the three buttons;
> get button response, decide what to do with file;

What would you do with the file in each case?

> if button == "Quit", save place in source file;
> next;

Make one directory with all the files (or with a symbolic links for each
file). Each time the program is invoked, take the first entry in the
directory and display it. Based on the response, either move it to the
accept directory or the reject directory (or move it to accept vs delete
it, whatever.) Since the file is no longer there, place is inherently
saved. Quit doesn't have to do anything, nor even have to exist--closing
the browser without responding is a form of quiting.

Or use a database.

Xho

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Posted by Rich Grise on April 2, 2008, 3:53 pm
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On Wed, 02 Apr 2008 04:07:42 +0000, xhoster wrote:
>> Apologies to Perl purists - comp.infosystems.www.authoring.cgi doesn't
>> work on my newsreader, and this is a CGI question:
>>
>> What I want to do is, I've got a large collection of image files:
>> $ wc gallery-pix
>> 37448 62619 3218967 gallery-pix
>>
>> and what I'd like to do is look at each of the 37488 image files on
>> some kind of page, with buttons like "Keep", "Skip", and "Quit",
>> so I can page through all of these images, which are strewn all
>> over the Samba server, and decide which ones might look good on
>> the website.
>>
>> So, is it possible to do something like (in pseudocode):
>>
>> for each $line in <file> {
>
> In CGI, your program won't survive for the loop to iterate. Unless
> you are making one page with all 37448 files on it.
>
>> show webpage with <img> tag, and the three buttons;
>> get button response, decide what to do with file;
>
> What would you do with the file in each case?
>
>> if button == "Quit", save place in source file;
>> next;
>
> Make one directory with all the files (or with a symbolic links for each
> file). Each time the program is invoked, take the first entry in the
> directory and display it. Based on the response, either move it to the
> accept directory or the reject directory (or move it to accept vs delete
> it, whatever.) Since the file is no longer there, place is inherently
> saved. Quit doesn't have to do anything, nor even have to exist--closing
> the browser without responding is a form of quiting.

Thanks - I really like this answer - I hadn't even consider loading up
a directory with symlinks.

I'm going to try this next, as a way to avoid slurping the whole file.

So, anybody got a quick and dirty script that will make 38,000 symlinks?
;-)

I'm not too worried about how long it will take - I'm doing this in
my "spare" time, and the boss doesn't bother me much as long as I look
busy. :-)

Thanks!
Rich



Posted by Jim Gibson on April 2, 2008, 6:53 pm
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>
> So, anybody got a quick and dirty script that will make 38,000 symlinks?

for my $i ( 1..38000 ) {
symlink( '/path/to/somefile', sprintf("symlink%5.5d",$i));
}

--
Jim Gibson

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