Welcome to the world of Bash, most widely used shell in Linux. Bash is surprisingly configurable, and, by the time you finish reading this article, you'll have an environment more comfortable for you. Bash does not differentiate between internal shell variables and external environment variables. A shell variable is a variable (usually all caps), associated with a value, and carried around between shells. Many programs use their own variables, like PILOTRATE, which they check. Bash has its own variables, like MAIL, that are important to it. Environment variables are set using the syntax:
export VAR=VALUEor in two lines:
VAR=VALUE export VARTo check the value of an environment variable, type echo $VAR, or to see all set variables, type env. bash executes your ~/.bash_profile file for the login shell (on the console), and ~/.bashrc for non-login shells (xterms and the like). Often you may just want to link one to the other. If you export a variable, or set an alias on the command line, it only stays active for that one bash session. You must put it in your login script for it to stick. If you start having a monolithic .bashrc file and want better organization, you can split it up. Often, people break up their .bashrc into aliases, variables and functions, and the .bashrc simply executes the others. To have your .bashrc execute other files put in a line like this:
The first environment variable we'll discuss is PS1. PS1 stores a character string that is interpreted by bash for use as your prompt. Here is a sample PS1 and its generated prompt:
Backslashed characters are interpreted, while other characters are displayed verbatim. \u is translated to user name, \h is translated to host name up to the first period, and \w is the working directory. Some of the most important backslashed characters, which can also be found in the bash manpage, in the PS1 section, are shown in the table “Interpreted Characters.”
One of the cool things in all X terminal emulators (xterm, rxvt, Eterm, ...) is that if you print "\033]0;STRING_HERE\007", the title of the term changes to STRING_HERE. Try it by typing:
echo -n "\033]0;Be Happy\007"
What I do with this is put a small function in my .bashrc function xtitle (see Listing 1), and I call this after I've set my PS1 variable, so at the end of my .bashrc file I have the line:
PS1=''\u@\h:\w>$'' xtitle export PS1This means that if I'm in a terminal emulator, it will set TITLEBAR, a string which will append user@hostname:directory to my prompt string (so it's printed each time I get a new prompt), and then export it. (Note that if your terminal emulator sets $TERM to something other then xterm* or rxvt*, you need to add another case, with | WEIRD_TERM_ENV on the line with xterm* | rxvt*) before the close parenthesis.
One of the most useful things to use with Bash is aliases. Aliases simply direct Bash to interpret a text string as something else. For example, you can fix it so that when you type happy, Bash interprets it as:
echo I'm a shiny happy shell
All aliases take the same form:
alias ALIAS="COMMAND"Often, you may want to change the default behavior of a command, such as ls. I alias ls in this way:
alias ls="ls -aF --color"ls now prints all files, in color, with classification. \ls will execute the unaliased command. Other times you may decide to define a whole new command in order to shorten the amount of repetitive typing. Here are a few aliases I use:
alias mkall=\ "./configure && make && sudo make install" alias whizz="ssh email@example.com" alias tgz="tar -xvzf" alias ll="ls -aFl" alias ls-d="ls -Sc"These all save time and keystrokes, and since anything you type after the alias is still passed to Bash, it will just translate the part that is aliased. In my case, executing tgz linux-2.2.14.tar.gz actually executes tar -xvzf linux-2.2.14.tar.gz.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide