filesystem

Synchronizing directories with Perl and SSH

For a while now I have been using ICQ both at home and at work. Instead of having two different copies of data or running ICQ remotely, I was simply copying all data files over between these two locations. rsync with scp were doing the job just fine. The problem emerged when I started to use ICQ on more than two machines (two machines in the office and one at home). I had to always figure out where is the latest copy of my data and distribute it from there to all the other locations. After doing it manually for just a couple of time bored me to death and I decided to write a script.

I started off with a very specific script that was only meant to copy my ICQ back and forth, but quickly realized that it can be generalized to copy any set of directories. So, here it is – sync_dirs.pl.

This script accepts and requires only one parameter – directory to synchronize. You can define a few shortcuts for frequently used directories inside the script. Locations are also defined inside the script. Since this piece of code uses Net::SSH and Net::SCP, the current limitation is that you must have ssh configured to authorize with keys, not passwords. The good news, is that you need only one location to be able to access all the others. The most recent copy of data will be copied over to this central location and from there distributed to all the other machines.

Recursively renaming files in Linux

One thing I liked about Linux is it’s hidden simplicity. When in a hurry, I usually go for the first working solution of a given problem. If the same problem appears often, I can get used to the first solution so much that I don’t even think about simplifying it.

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Finding files in Linux

Many beginning Linux users experience difficulties getting used to the filesystem structure. Indeed, there are many files and directories, the structure of which are not as obvious as it could be. Choosing an appropriate location for a new file or directory is difficult and many choose to follow their own instincts.

With more experience, the file hierarchy becomes clearer and old concepts of placing files and directories start to fade out. When it happens, finding things becomes difficult. It is than that users learn that Linux has many tools for finding things. And it is than that they become confused once again.

Read on for a quick introduction into searching tools available in Linux.

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Working with named pipes in Perl

The collegue of mine came across a problem that developed into an interesting solution that I decided to share with the world. Actually, I think the world is pretty much aware of the solution, but just in case that I will ever be looking for this solution again, I’ll have it handy here.

The task at hand was to do some processing of the logs on the fly. The syslog was configured to filter the appropriate logs into a named pipe and a Perl script was written to read from the said pipe and do all the processing.

The original piece of code looked something like this:

open (SYSLOG, "<$named_pipe") 
  or die "Couldn't open $named_pipe: $!\n";

while () {
  do_processing($_);
}

close(SYSLOG);

The problem came with syslog daemon restarts. Every time the syslog was stopped, the EOF was sent to the pipe and the script stopped reading it.

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