Entries Tagged 'Unix' ↓

I've recently decided to give Mac OS X a try. For the past week or so I've been spending a good few hours a day working in Snow Leopard installed on a MacBook Pro borrowed from a friend.

While Mac OS is unlike any Unix-like operating system I've managed so far, there are certainly some of similarities. I can honestly say that I'm enjoying the Mac Book Pro so far, and hope to discover most of the differences compared to my previous Unix-like desktop which is Ubuntu 9.10.

Mounting NFS on MAC OS X

One thing which I noticed immediately was that out of the box it was impossible to mount any NFS shares from my Ubuntu NAS server. Any attempt to mount a remote filesystem would give me an error like this:

mbp:~ root# mount nasbox:/try /mnt
mount_nfs: /mnt: Operation not permitted

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Hi everyone!

I'm back from my holidays, and it's time to open the Unix Tutorial members area for new registrations once again!

If you're still looking for a reason to become a member – please read the Becoming a Unix Tutorial member post.

This time around, new users will receive a life-time access to just one course, the Unix foundations one. This is going to be a constantly updated and expanded course so I'm sure you'll benefit from revisiting it now and then. New courses added at a later stage will never be available for free: I plan to make them very specialized and will charge for access – more on this later.

Wait no more – here's your chance to join: Unix Tutorial members sign-up. I don't have nearly as much time to further develop the course, but please take time to leave a comment to this post or update a thread on the Unix Tutorial members discussion board about what exactly you're interested in.

Although I've already shown you how to sum numbers up in bash, I only covered the bash way of doing it. I really like scripting with bash, but when it comes to calculations, there's quite a few important features missing from bash, and fixed point (thanks for the correction, Azrael Tod!) calculations is one of them. Fortunately, bc command comes as a standard in most Unix distros, and can be used for quite complex calculations.

Basic calculations with bc

bc is a very simple command. It takes standard input as an expression and then evaluates this, performing all the necessary calculations and showing you the result. Thus, to quickly sum numbers up or get a result of some other calculation, simply echo the expression and then pipe it out to the bc command:

ubuntu$ echo "1+2" | bc
3

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One of the really useful features almost every Unix shell has is support for command aliases – a way to run a command or a series of Unix commands using a shorter name you get associated with such commands.

An example of a command alias in Unix shell

Here's one of the most useful aliases I have for Solaris systems:

solaris$ alias ls='/usr/local/gnu/bin/ls --color -F'

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If you're ever thought of summing up more than two numbers in shell script, perhaps this basic post will be a good start for your Unix scripting experiments.

Basic construction for summing up in shell scripts

In my Basic arithmetic operations in Unix shell post last year, I've shown you how to sum up two numbers:

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Today I was working on a script, and one of the subroutines needed simple seconds-based arithmetics with time. As you probably remember from  my date and time in Unix scripts article, the easiest way to approach this task is to deal with the raw representation of date and time in Unix – the Unix epoch times. This post will show you how to convert standard dates into Unix epoch times in Perl.

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I've just been asked a question about changing the ownership of files from one Unix user to another, and thought it probably makes sense to have a quick post on it.

File ownership in Unix

Just to give you a quick reminder, I'd like to confirm that every single file in Unix belongs to some user and some group. There simply isn't a way to create a file without assigning ownership. I've briefly touched the topic of confirming file ownership in Unix before, so today I will simply build on that and show you how to change ownership of files.

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It's not often that I write about Perl Scripting on Unix Tutorial, but that's just because I don't script in Perl this much on a regular basis. Today, however, I'd like to share one of the building blocks – a really basic piece of functionality which you'll find really useful in almost any Perl script.

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As you know, every file in your Unix OS belongs to some user and some group. It is very easy to confirm the ownership of any file because user id and group id which own the file are always linked to the file. However, sometimes you can't tell which user owns the file, and today I'm going to explain why. It's a rather lengthy post and a complicated matter, so please leave questions or comments to help me polish this article off.

Files and directories ownership in Unix

If you look at any file using ls command, you will see an output like the one shown below – it reveals file access permissions, user and group id of the owner, the modification timestamp and the file name itself:

ubuntu$ ls -l /tmp/myfile
-rw-r--r-- 1 greys admin 0 Jan  6 03:51 /tmp/myfile

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In my first introductory rsync post, How To Synchronize Directories with Rsync, I've shown you the most basic approach to syncing two directories up. Today, I'd like to show you another useful thing you can do with rsync.

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