Question

CGI/Bash/Shell: Echoing to a HTTP server (display a page on a server)

Asked by: Don_T

Hi
I'm creating a pipeline to process a HTML form on a server. I read the text input to a file via $QUERY_STRING (works), do some processing in Python and Prolog (works) and after that I want the script to display the results in a HTML page. How can that be done? Echoing doesn't seem to work. Do I have to set the STDOUT somehow and is it possible at all?

Using PHP would be a lot simpler, but shell_exec() doesn't execute the subprocesses of the bash script (Python/Prolog) properly. F.e. for the Prolog script it just displays the output of the write('') - instructions, but does not actually execute the calculations/manipulate the according files.

#!/bin/sh
 
echo $QUERY_STRING | sed -r "s/.*=//g" | sed "s/+/ /g"  ... > input.txt
 
echo 'Preprocessing'
python ...
sh ...
swipl ... 
echo 'Processing'
swipl ... (creates out.txt)
...
echo 'Done.'
->now display out.txt to the user

                                  
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Asked On
2009-06-14 at 07:40:11ID24490323
Tags

cgi

,

bash

,

shell

,

pipeline

Topics

CGI Scripting

,

Bourne-Again Shell (bash)

,

Bourne Shell (sh)

Participating Experts
4
Points
125
Comments
13

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Answers

 

by: bs98909Posted on 2009-06-14 at 07:48:31ID: 24623644

well you are writing to a .txt file. You have access to the server so you will have to write to the webpage location to an "html" file and in that file you wil have to out put the lines like below.

Then you should see your out if that all works. Granted you can see the txt file if your web server allow it.

echo "<html>" > out.html
echo "<header>" >> out.html
echo "</header>" >> out.html
echo "<body>" >> out.html
echo "--- this is your output here --" >> out.html
echo "</body>" >> out.html
echo "</html>" >> out.html

                                              
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by: Don_TPosted on 2009-06-14 at 08:13:12ID: 24623736

I can create the HTML page and look at it by entering the according URL in the browser after processing has finished; my question is how do I display the page to the user from within the script after processing?
cat ../out.html doesn't work.

A nasty hack would be a delayed http redirect from the page containing the form to out.html... but I would like to do it from within the script.
cheers

 

by: bs98909Posted on 2009-06-14 at 08:23:58ID: 24623778

how about as a form then? Have the process be done when the user clicks the submit, and the get/post is then the output of the scripts?

 

by: Don_TPosted on 2009-06-14 at 08:36:41ID: 24623817

I have an input form, and the script is executed when user presses Submit. I use GET to get the input, which is then processed by the script:

<form method="GET" action=".../cgi-bin/test.sh">
...
<textarea name="text"><!--input--></textarea>
...
<input value="Proceed" style="width: auto; float: right;" type="submit">

->and the get/post is then the output of the scripts?
You mean I should create a URL with something like ?output=... and put the output there?
I can't do that, because the output is HTML formatted (text is color highlighted etc.) and can be quite long.

what I need is a command for the server side sh script that displays the out.html page to the user..

 

by: Don_TPosted on 2009-06-14 at 08:52:27ID: 24623856

Ok, I can call a perl file with

#!/usr/bin/perl

print "Location: http://newdomain.com/output.html\n\n";

in it at the end of the script. that works,
I'm still interested if there's a way to do it from the sh script directly...
cheers

 

by: bs98909Posted on 2009-06-14 at 09:07:12ID: 24623900

So what is in the Perl script that you are not coding with your HTML?

I guess that this is where I am getting confused. The output of the scripts that you are running all create some output. That text output needs to be display in HTML which is where the shell scripting comes into play to merge the output into an HTML file, correct?

You can make the output file a server side include (.shtml) and then just use a like like:
<!--#include file="out.txt"-->

 

by: TintinPosted on 2009-06-14 at 14:36:58ID: 24625281

Your problem is most likely to do with relative paths, ie: ../out.html is probably not the correct path to the output in the CGI context.  You can either try using an absolute path or determine the correct relative path.

 

by: kolotseyPosted on 2009-06-17 at 11:41:31ID: 24651217

It seems that your problem is you doesn't send HTTP headers in your response. When cgi-script is  executed HTTP headers aren't usually sent by server. So you have to send them from your script.

Try something like this:

#parsing query...
#processing...

printf "HTTP/1.1 200 OK\r\n"
printf "Content-Type: text/html\r\n"
printf "\r\n"

#your other output

By the way, you shouldn't send any date before you have sent headers.
Futher reading: http://linux-programming.ru/shell-script/working-with-network-in-shell/

 

by: Don_TPosted on 2009-06-24 at 02:59:01ID: 24699619

Hi

bs98909: -> correct. But I need to redirect the user to the generated results page (.shtml/include or similar) somehow. This is where the Perl "script" (actually just the 'print "Location: http://newdomain.com/output.html\n\n";') comes in.

tintin: the out.html page is creted in the www folder of the server, and I can look it up manually, when processing has finished. so this should be fine.

kolotsey: that doesn't seem to work; where do I send the printf commands to? to the cgi folder of the server? or www folder?

Here's the architecture of the pipeline:

1. HTML GET -> calls -> sh script
2. sh script -> creates input file from GET, initiates and organizes calculations (python, prolog)
3. sh script -> then takes result file of the subprocesses (python,prolog) and copies them into out.html to the www folder of the server
4. sh script then calls the perl file redir.pl, which simply states: print "Location: http://mydomain.com/output.html\n\n"; to redirect the user to out.html in www folder.

its step 4 that is/was my problem! how do I redirect the user to the results page from thesh script? maybe there is a way with netcat?

 

by: Adam314Posted on 2009-06-25 at 09:12:41ID: 24712946

For step 4, you could use this:
    #!/usr/bin/perl
    use CGI ':standard';
    print redirect('http://mydomain.com/output.html');

Instead of a perl script, you create a file that contains the needed data, then cat that file.  This would have less overhead than starting perl.  To do this, put the above code in a file, and run it like so:
    ./script.pl > /path/to/www/redirect_header.txt

Then, have your sh script cat it like so:
    cat /path/to/www/redirect_header.txt

 

by: kolotseyPosted on 2009-06-26 at 01:52:43ID: 24719213

Don_t: I second Adam314's comment but instead of printing headers to a temporary file and then cating it, use my example. You SHOULD send headers directly to the output, server then will send headers straight to the client (web-browser).


step 2. sh script -> creates input file from GET, initiates and organizes calculations (python, prolog)
Here are modifications:
step 3. Instead of copying result, do the following:
#print headers on you sh script, server will send this lines to client (web browser)
printf "HTTP/1.1 200 OK\r\n"
printf "Content-Type: text/html\r\n"
printf "\r\n"
#cat result of python script to stdout
cat /tmp/result.txt

20120131-EE-VQP-002

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