Entries tagged as console

Shell trick #1: Numbering lines in text files

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Hi, today I'll present you something new. It is an experiment and I'd be curios whether you like it. I've started a little series of ttyrecs. That means, I've recorded a little tip or trick on the console and uploaded it to PLAYterm so it can be easily played back in the browser. I thought it could be useful to do a little command line gymnastics.

Today I'll show you three ways how you can number lines in text files. We'll do that with cat, nl and vim.

Note: you need JavaScript enabled in order to play the ttyrec.

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Grep's out of date? Full ACK!

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grep is a handy tool and I use it every day. But sometimes I wish it had some more features. For instance full featured Perl compatible regular expressions (PCRE) since the current implementation is not complete and I think it will never be, automatic recursive search, exclusion of non-text files etc.

Here a tool called ack comes into play. It's a search tool and grep replacement written in Perl, which is able to do all these things. Guess what!

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#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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#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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#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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#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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#14: Using screen

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If you work on remote servers via SSH and don't want to open multiple connections, or if you don't have a graphical terminal emulator and don't want to open several concurrent ttys, screen is the right tool for you.

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#11: Understanding Linux man pages

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man is probably one of the most used Linux commands at all. Less known, however, is that man is more than just man.

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#10: Using xargs

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One very helpful tool that exists on many Unix-like systems is xargs. xargs is built to receive standard input (STDIN) and pass it as command-line parameters to a specified command.

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#8: Advanced usage of grep

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grep is probably one of the best known, or let's better say: the most used command line tools on UNIX systems. But not many people know that it is so much more than just a very simple text search command.

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#7: Job control and background processes

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Linux is a multitasking operating system, so you can execute several programs at once. It is also possible to make use of this on the console.

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#5: Be careful with locate

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When locating files on your disk locate is a nice tool because it indexes your hard drive and therefore finds files very quickly. But locate can also be a great security threat to your system.

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