Entries filed under category “Advent calendar 2010”:

#24: The awk basics

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awk is very complex and hard to learn. It is the most difficult task in Linux administrator's lives and drives everyone crazy who tries to learn it. It's written by Gods and used by them, no mortal man can ever learn awk.

In fact…, no! If you know any C-like programming language and regular expressions, awk is absolutely easy and it can make things much easier. It's pretty mighty, but I've never seen any programming language easier than awk (except QBasic).

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#23: File descriptors

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File descriptors are very essential in programming. When you open a file, you get a token, which identifies the file instance. With this token you refer to the file, write, read or close it. You have about the same on the shell.

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#22: Processes with high and low priority

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Processes in Linux may run with different priorities so that important processes get more CPU time than less important ones. This priority is called the “nice value” or ”niceness” (NI). The nice value is a number between -20 and +19 with the default value right in the center at 0. The higher this nice value, the “nicer” a process is to others, i.e., the lower its priority.

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#21: The command line calculator bc

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Performing calculations on the command line is very handy and bc is the tool which does it for you. Also bash can do some calculation stuff, but that's not very intuitive. Bash is built for different things than calculation and so bc is the better choice. It can do much more for you and its syntax is ways easier.

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#20: Multi-line sed search and replace

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sed is built to process strings (either from STDIN or from a file) line by line. Therefore, you can't search for multiple lines. But there are several ways to work around this. I'll be showing you three ways of performing multi-line replacements.

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#19: Label partitions

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On Linux devices and their partitions are named automatically when being plugged in. They have a base name (for SCSI devices it's sd), a device identifier (a lowercase letter) and a number for every partition. These names depend on the order in which the devices are plugged in, so they are not static at all.

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#18: GNU find operators

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This is not a tutorial about find in general as you might expect it. find, and the GNU variant in particular, is very complex and can't be covered in one short blog post and actually, there are many good tutorials on the Internet. Instead, this blog post concentrates on one single aspect of find: operators.

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#17: Process substitution

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You probably know command substitution. Command substitution executes a command and uses its output as a variable on the shell. The operator for this is either the backtick operator. But did you also know that there is a counterpart of command substitution? This counterpart is called process substitution.

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#16: Introduction to lsof and fuser

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You've probably heard of lsof and fuser. Since on UNIX systems everything is a file, these tools are absolutely important to know for each system administrator. They can make your work easier and they can also help identifying attacks on your system.

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#15: Named and unnamed pipes

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Pipes are used very often on UNIX systems. They connect two programs in that way that the STDOUT of the first program becomes the STDIN of the second program.

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