Entries Tagged 'Unix' ↓

Hi! If you're new here, you may want to subscribe to the Unix Tutorial RSS feed to get regular tips & tricks for all flavors of Unix. You can follow me on Twitter, too! Thanks for visiting!

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

Continue reading →

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'

Continue reading →

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:

 Continue reading →

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.

Continue reading →

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.

Continue reading →

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.

Continue reading →

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

Continue reading →

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.

Continue reading →

When I was writing a post about using date command to confirm date and time in your Unix scripts, I made a note in my future posts list to cover the date calculations – finding out the date of yesterday or tomorrow, and so on. Today I'll show you the simplest way to calculate this.

Continue reading →

Today I'd like to expand a bit more on the basic calculations in Unix scripts.

Use Parenthesis to simplify math expressions

In Basic Arithmetic Operations post I've shown you how expression evaluation can be used to calculate simple math expressions in your Unix shell:

ubuntu$ START=1
ubuntu$ FINISH=10
ubuntu$ ELAPSED=$(($FINISH - $START))
ubuntu$ echo $ELAPSED
9

Continue reading →