Entries Tagged 'Unix' ↓
May 7th, 2008 — Basic stuff, Scripts, Unix
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Any Unix shell script longer than a line will most likely involve using variables. Variables are used to store temporary values to simply using them in various Unix commands of your script. The beauty of using variables is that they can be evaluated and set ones, but then reused as many times as you like without your shell interpreter having to re-evaluate them again.
Defining a variable in Unix shell
To specify a value for a variable, you need to decide on the variable name - can be any word or combination of English alphabet symbols and digits, and specify the value.
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February 14th, 2008 — Basic stuff, Unix
I can see some of you have arrived to my Unix file types post looking for an example of using symlinks in Unix. Today I would like to give you a quick introduction into Unix symlinks.
What is symlink?
Symlink is a short name for symbolic link (sometimes also referred as soft link) is a special type of file in Unix, which references another file or directory. Symlink contains the name for another file and contains no actual data. To most commands, symlinks look like a regular file, but all the operations (like reading from a file) are referred to the file the symlink points to.
February 12th, 2008 — Perl
A few months ago, I've given a really simple example of using Perl for parsing directory trees in Unix. If you looked closer at it, you would have noticed that the script was working fine, but showing file modes as strange large numbers which didn't look like the usual file permissions you would expect. Today I'm going to explain why this happens, and show you how to find out a user type in Perl.
lstat and stat functions, return, among other things, the file mode value. While it looks confusing initially, it is in fact quite simply a combination field, which includes both the file type and all the permissions for it. If you print this field as a single decimal number, you will not recognize it, but if you simply convert it to octal, you will immediately start seeing the pattern:
Mysterious mode 33261 from the example below becomes 100755 when converted into octal, and you can easily see then the permission part of it: 0755.
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January 15th, 2008 — Basic stuff, Unix
I've noticed how many people found other pages of this blog trying to find more information about Unix sockets, and so I thought it's about time we shed some light on this seeming mysterious, but really simple concept.
What is a Unix socket?
A Unix socket (the technically correct name for it is Unix domain socket, UDS) is a way of inter-process communication (IPC) in Unix. Like almost everything in Unix, a socket is a file. It's a special file, to be precise. Unix processes which want to communicate between each other use special set of functions to access the special file of a Unix socket, and easily exchange data in both directions.
In very simple terms, a Unix socket is nothing but a byte steam - a data transfer between processes running locally or on networked Unix systems.
January 2nd, 2008 — Basic stuff, Unix
Finding the compiler version in your Unix system should be the first step before you attempt to compile any package from its source codes. In fact, if you're familiar with the common compilation routine, the configure script which you run to generate the Makefile before compiling anything does exactly that - it finds out which compilers (if any) you have installed on your system, and confirms their versions and capabilities.
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December 14th, 2007 — Unix
Quite often there's a need for you to take a screenshot of your Unix desktop, and as always there's a number of ways to do it. Today I'm going to cover the command line approach to taking screenshots.
Taking a Screenshot with xwd
Most modern Unix desktop systems come with Gnome desktop environment by default, and use Xorg as their default X11 server. This means you are likely to have the xwd tool in your OS, which allows you to take screenshots.
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November 8th, 2007 — Scripts, Unix
I had a need to scan a huge directory tree today, identifying the users and Unix groups owning all the files. The problem I faced was too long usernames and group names which meant the
find /directory -ls
command which I normally use for such tasks wasn't terribly useful because there was no space delimiter between a username and a group. Results of such scan of the directory tree will have to later be parsed by other tools, and that's why proper splitting of the output into separate fields is so important.
This issue was motivational enough to refresh my Perl skills and sketch the following script (based entirely on this Never Run Unix Find Again article).
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September 25th, 2007 — Basic stuff, Unix
In Unix systems, there are 6 file types. Below I will give a very short description of each.
How to find out the type of file in Unix
The first and most obvious way to confirm the type of a particular file is to use the long-format output of ls command, invoked by the -l option:
$ ls -l *
-rw-r–r– 1 greys greys 1024 Mar 29 06:31 text
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September 11th, 2007 — Advanced topics, Linux, Unix
I've recently upgraded Apache and PHP on my VPS, and one of the unpleasant surprises was that some scripts which tried including pages from remote sites (I know, not the most secure approach, but there were reasons for that) got broken.
allow_url_fopen
Traditionally, all the websites Google finds suggest that you double-check that your php.ini config has the allow_url_fopen enabled:
allow_url_fopen = On
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