Web Conference 2004

Writing Perl/CGI Scripts for ITS/ASET Web services

Using Data files

One of the first things you will want to do with a dynamic content Web page is to save data on the server for later retrieval. There are various ways to do this, including databases. But first let's start with the oldest and simplest way, using files.

Reading a file

First let's read a file and send it to the browser.

#!/usr/local/bin/perl

print "Content-Type: text/html\n\n";

open(FILE,"example.html") or webdie("Cannot open example.html: $!");

while(<FILE>){
        print;
}

close(FILE);

exit 0;

sub webdie {
        print "<html>\n";
        print "<body>\n";
        print "<p>Error: $_[0]</p>\n";
        print "</body>\n";
        print "</html>\n";
        exit 1;
}

Run readfile.cgi [download]

Writing to a file

Writing a file is similar to reading a file. You use the open() function, but with the > symbol in the filename to indicate you want to write to it. Then use print FILE to print to the FILE filehandle.

#!/usr/local/bin/perl

print "Content-Type: text/html\n\n";

$datafile = "write2file.dat";
open(FILE,">$datafile") or webdie("Cannot open $datafile for writing: $!");

print FILE "Check, check...is this mic on?\n";

close FILE;

# now tell the browser what you did

print <<END;
<html>
<body>
<p>$datafile was written</p>
</body>
</html>
END

exit 0;

sub webdie {
	print "<html>\n";
	print "<body>\n";
	print "<p>Error: $_[0]</p>\n";
	print "</body>\n";
	print "</html>\n";
	exit 1;
}

Run write2file.cgi [download]

Check, check...is this mic on?

Setting permissions to allow test.scripts.psu.edu to write files

To give the script server the ability to save changes to individual files that already exist, do the following:

Login to the ACL Explorer (via https://www.work.psu.edu/)
Navigate to your working Web folder as you did to make files executable, and select the file you want to save changes to.
In one of the bottom two rows of the ACL table, select "group" from the pull-down menu (set to "user" by default).
Type in test.scripts.psu.edu in the field next to it.
Check the boxes for Read and Write permissions next in the same row.
If the mask_obj restricts either Read or Write, enable them for mask_obj as well.
If the other_obj restricts either Read or Write, enable them for other_obj as well. - This is actually a requirement of Apache, not necessarily used by the PASS permission system to grant access to the Web server process.
Click the Modify Access button.

To give the script server the ability to create and change any file in a folder, do the following:

Login to the ACL Explorer (via https://www.work.psu.edu/)
Navigate to your working Web folder as you did to make files executable, and select the folder in which you want to create and modify files.
If you want to grant access to change existing files as well, click Hide Files. Otherwise you can only create new files (although you can delete other files).
In one of the bottom two rows of the ACL table, select "group" from the pull-down menu (set to "user" by default).
Type in test.scripts.psu.edu in the field next to it.
Check the boxes for Read, Write, eXecute, Insert and Delete permissions next in the same row.
If the mask_obj restricts any of Read, Write, eXecute, Insert or Delete, enable them for mask_obj as well.
If the other_obj restricts any of Read, Write or eXecute, enable them for other_obj as well. - This is actually a requirement of Apache, not necessarily used by the PASS permission system to grant access to the Web server process. Because of this, Insert or Delete don't matter for other_obj (but don't hurt either).
Click the Modify Access button.

It is wise to grant these permissions on a separate folder than the folder where CGI scripts reside to prevent them from being altered by someone else using the servers.

Saving parameters to a file

Let's do a simple log script. Save the parameters as they come and the time and IP address.

#!/usr/local/bin/perl

use CGI qw(:param);

print "Content-Type: text/html\n\n";

$logfile = "log2file.log";
open(FILE,">>$logfile") or webdie("Cannot open $logfile for appending: $!");

# localtime() - get today's date, in our local timezone
#
#    0    1    2     3     4    5     6     7     8
# ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);
#
# $year - is number of years since 1900
# $mon  - is number of months after January
# Other fields are in the format we want.

@localtime = localtime();

# this is the same as $localtime[5] = $localtime[5] + 1900;
$localtime[5] += 1900; 
# this is the same as $localtime[4] += 1;
$localtime[4] ++;

# $datestamp - what is today's date, in YYYY/MM/DD-HH:MM:SS format
#
# sprintf("format","var1","var2"...) - output a scalar in the prescribed format
# %d - output the next variable in the list as a digit
# %2d - same as %d, but if less than 10, add a leading space
# %.2d - same as %d, but if less than 10, add a leading 0 
# %4d - same as %2d, but save room for 4 digits, not just 2

$datestamp = sprintf("%4d/%.2d/%.2d-%.2d:%.2d:%.2d", $localtime[5], 
  $localtime[4], $localtime[3], $localtime[2], $localtime[1], $localtime[0]);

# you can also do the above with:

$datestamp = sprintf("%4d/%.2d/%.2d-%.2d:%.2d:%.2d", reverse @localtime[0..5] );

# log the time
print FILE "$datestamp: ";

# log the IP address
print FILE "$ENV{'REMOTE_ADDR'} ";

# log the paramters sent
foreach $parameter (param()) {
	print FILE "Parameter($parameter) = \"" . param($parameter) . "\", ";
}

print FILE "\n";

close FILE;

# now tell the browser what you did

print <<END;
<html>
<body>
<p>Your parameters have been logged</p>
</body>
</html>
END

sub webdie {
	print "<html>\n";
	print "<body>\n";
	print "<p>Error: $_[0]</p>\n";
	print "</body>\n";
	print "</html>\n";
	exit 1;
}

Run log2file_clean.cgi [download]

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If you have any questions, feel free to ask me - mailto:jcd@psu.edu

Last update on: Monday, 14-Jun-2004 14:32:50 EDT