My 2 paisas

Archive for the ‘programming’ Category

I had used wget and downloaded all the java videos from the java tutorial site( and also all the other files on the website). There were around 20 of them. The problem was that the lectures were each present in a separate folder and I had to traverse to each of them to watch them. So I thought of writing a script which would search the main directory recursively for the lectures and then copy it in a specific folder. Luckily in my case each of the lecture were named differently and hence I didnt have to rename them and there were no issues of file name getting clashed. Below is my shell program:

#!/bin/sh

list=$`find . -type f | grep ".mp4"`
cp $list ./lectures

This would search all the files which had .mp4 in their name and copy them into the folder lectures.

Below is a one line command to display all the entry in @INC array which contains the paths where perl programs looks for perl modules.

perl -e ‘foreach $_ (@INC){ print $_,”\n”};’

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It is sad that I have found this solution after so many days. It is more sad that I never tried to look for this solution earlier. I must have found it atleast 3 months ago. Anyways now that I have found it, let me tell you what exactly I want to do and how the simple script helps me do it.

I have been playing with qmail and qpsmtpd from last 3-4 months. Now to test my set-up, I used to telnet to the port and then used to enter different telnet commands and used to watch the logs simultaneously to get errors.
Now everytime I used to enter the commands manually and that too I couldnt just go to history and execute it as telnet does not support storing commands in history.
Anyway finally today I got fed up of it and I thought let me see if there is a solution so that I dont have to enter commands manually. I didnt expect a solution. But when I searched for it, I found that it was so easy to do it. You just need to execute the following command.
./smtp.sh | telnet

and the contents of smtp.sh is given below:
#!/bin/sh
host=127.0.0.1
port=25
echo open $host $port
sleep 10
echo helo deeproot.co.in
sleep 10
echo mail from:test2@domain
sleep 10
echo rcpt to:test3@domain
sleep 50
echo data
sleep 10
echo checking
echo .
sleep 10
echo quit
#end

You can customize the script to anything that will make your life easier with telnet. I found this solution here, http://www.linuxforums.org/forum/linux-programming-scripting/92466-telnet-script.html

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If you know the name of the function and you want to see the man page for that function, then you can use the following command.

perldoc -f “function name” //without quotes

for example,

perldoc -f our
perldoc -f sysopen

This is one of the errors that I got when I started using perl modules.
It was because I had not put “1;” at the end of my perl module. So I did not get the error after I put “1;” at the end of the perl module.

why is the “1;” necessary at the end of perl modules?

Typically, a module contains a bunch of subroutine definitions.  A
module may also contain code which is not part of a subroutine. This
code is executed at the time the module is loaded, so it can be used
to initialize the module. For example, the module might open
adatatbase connection or initialize some time at the time it is
loaded.


Such code might be successful, or it might fail. Perl allows the
module to indicate the result by returning a true or false value back
to its caller. If the value is false, Perl aborts the compilation
with an error message.

Unfortunately, the default return value is *false*, so a module which
just defines a bunch of subroutines, and which has no initialization
code, accidentally returns a false value back to the caller, and Perl
aborts. So we insert "1;" at the end to suppress this misbehavior.

http://dev.perl.org/rfc/269.pod
http://dev.perl.org/rfc/269.html

discusses this in some more detail.

For documentation, see perldiag:

%s did not return a true value
(F) A required (or used) file must return a true value
to indicate that it compiled correctly and ran its
initialization code correctly. It's traditional to
end such a file with a "1;", though any true value
would do. See the require entry in the perlfunc man-
page.

and the relevant part of 'perlfunc':

The file must return true as the last statement
to indicate successful execution of any initialization code, so
it's customary to end such a file with "1;" unless you're sure
it'll return true otherwise. But it's better just to put the
"1;", in case you add more statements.

Courtsey: http://lists.netisland.net/archives/phlpm/phlpm-2001/msg00426.html
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