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A Guided Tour Of Awk
Greg Goebel has written a pretty extensive overview of the awk command over at vectorsite. As it’s one of the best ones I’ve seen floating around on the net I’ve included it here:
The Awk text-processing language is useful for such tasks as:
- Tallying information from text files and creating reports from the results.
- Adding additional functions to text editors like “vi”.
- Translating files from one format to another.
- Creating small databases.
- Performing mathematical operations on files of numeric data.
Awk has two faces: it is a utility for performing simple text-processing tasks, and it is a programming language for performing complex text-processing tasks.
The two faces are really the same, however. Awk uses the same mechanisms for handling any text-processing task, but these mechanisms are flexible enough to allow useful Awk programs to be entered on the command line, or to implement complicated programs containing dozens of lines of Awk statements.
Awk statements comprise a programming language. In fact, Awk is useful for simple, quick-and-dirty computational programming. Anybody who can write a BASIC program can use Awk, although Awk’s syntax is different from that of BASIC. Anybody who can write a C program can use Awk with little difficulty, and those who would like to learn C may find Awk a useful stepping stone, with the caution that Awk and C have significant differences beyond their many similarities.
There are, however, things that Awk is not. It is not really well suited for extremely large, complicated tasks. It is also an “interpreted” language — that is, an Awk program cannot run on its own, it must be executed by the Awk utility itself. That means that it is relatively slow, though it is efficient as interpretive languages go, and that the program can only be used on systems that have Awk. There are translators available that can convert Awk programs into C code for compilation as stand-alone programs, but such translators have to be purchased separately.
One last item before proceeding: What does the name “Awk” mean? Awk actually stands for the names of its authors: “Aho, Weinberger, & Kernighan”. Kernighan later noted: “Naming a language after its authors … shows a certain poverty of imagination.” The name is reminiscent of that of an oceanic bird known as an “auk”, and so the picture of an auk often shows up on the cover of books on Awk.
Basics of MySql on the Commandline #3
In this tutorial we’re going to cover how to Alter Records, Update Records, and how to Delete Records.
Please see these prerequisites:
Basics of Using Grep
Grep is a command line utility that was originally written for use with the Unix operating system. Given a list of files or standard input to read, grep searches for lines of text that match one or many regular expressions, and outputs only the matching lines.
Grep allows you to search files for symbols or strings (groups of characters like words) and will return the files that the search sting is found in. For example you want to search a website’s access log file for a recent traffic that came from a search engine. Most search engine referral urls have a question mark in them. The Grep command would look something like this:
grep [search string] [file name]
Basics of MySql on the Commandline #1
MySQL is a multithreaded, multi-user SQL database management system (DBMS) which has more than 11 million installations. The basic program runs as a server providing multi-user access to a number of databases.
Originally financed in a similar fashion to the JBoss model, MySQL was owned and sponsored by a single for-profit firm, the Swedish company MySQL AB, now a subsidiary of Sun Microsystems, which holds the copyright to most of the codebase. The project’s source code is available under terms of the GNU General Public License, as well as under a variety of proprietary agreements.
This tutorial is to get you familiar with the basics of mysql. It is not meant to be an end-all resource, but a starting point. Later we will discuss more advanced functions of mysql and how to manage databases via web interfaces such as phpMyAdmin.
(Video to Come)
Understanding /etc/passwd, /etc/group, /etc/sudoers, and /etc/skel/
I decided to write this as a subsection of Root, Superuser, and User Management Basics as that was getting rather lengthy. There is a bit more to understand about managing users, groups, and super-user permissions. We’ve already covered how to add a user, delete a user, add a group, delete a group, rename a group, and how to reset a user’s password. Now what we didn’t go into depth was, all of this information is controlled by a number of files and these commands modify these files. These files can be manually editted though to accomplish the same thing or for more detailed management.
How to Use vi
From wikipedia: vi is a screen-oriented text editor written by Bill Joy in 1976 for an early BSD release. The name vi is derived from the shortest unambiguous abbreviation for the command visual in ex; the command in question switches the line editor ex to visual mode. Current releases of vi are free and open source software, usually released under permissive free software licenses> such as the BSD License. vi is the commandline text editor of choice (well, not if you ask the emacs crowd), but the reason for it’s widespread use is that it can fit on a floppy disk to aid system recovery. It is a power editor with many options to navigate and manipulate text and we’ll covers the basics here.
Download the Cheat Sheet: vicheatsheet.pdf (source )
The basics of ftp and sftp
There’s many ftp clients on all operating systems, but in the Linux world we come across many machines where we have no gui interface and it’s helpful to have the knowledge on how to utilize ftp and ssh’s secure implementation, sftp, on the command line. FTP functionality comes built into most linux systems and you should not have to install anything to get started here.
Basics of ssh and scp
What is OpenSSH? According to the OpenSSH page: OpenSSH is a FREE version of the SSH connectivity tools that technical users of the Internet rely on. Users of telnet, rlogin, and ftp may not realize that their password is transmitted across the Internet unencrypted, but it is. OpenSSH encrypts all traffic (including passwords) to effectively eliminate eavesdropping, connection hijacking, and other attacks. Additionally, OpenSSH provides secure tunneling capabilities and several authentication methods, and supports all SSH protocol versions. The OpenSSH suite replaces rlogin and telnet with the ssh program, rcp with scp, and ftp with sftp. Also included is sshd (the server side of the package), and the other utilities like ssh-add, ssh-agent, ssh-keysign, ssh-keyscan, ssh-keygen and sftp-server.
OpenSSH is developed by the OpenBSD Project. The software is developed in countries that permit cryptography export and is freely usable and re-usable by everyone under a BSD license.
General speaking it is the remote terminal connection of choice. In this entry we are only going to cover the very basics of ssh and scp. We will cover more advanced features and sftp in later entries.
Encrypt files with OpenSSL
Need to protect sensitive information? Then you need an encryption program. Luckily most linux distrubtions come with openSSL already installed. I’ve tested this on openSuse and Ubuntu and both seem to have the package right out of the box.
To encrypt a file: openssl des3 -salt -in existing_file.txt -out file.des3
The above will prompt for a password, or you can put it in with a -k option (as shown below), assuming you’re on a trusted server.
To Decrypt: openssl des3 -d -salt -in file.des3 -out file.txt -k mypassword
Need to encrypt what you type? Enter the following, then start typing and ^D to end.
$ openssl des3 -salt -out new_file_name.txt
Also See: