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--- blog:spring2016:mpotapen:journal [2016/03/01 04:54] – [A Variety of Things About Linux in General] mpotapen
+++ blog:spring2016:mpotapen:journal [2016/05/11 15:51] (current) – mpotapen
@@ Line 145: / Line 145: @@
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+====Week 6====
+===Killing Things===
+This week Matt taught us how to kill things like a ninja. The Unix operating system supports various signals that can be sent to programs. I've had some experience with signals when programming with the gtk package in my previous adventures in which I attempted to create windowed programs. The code must be written in order to handle the signals and act on them properly. In Unix, there are 64 signals that can be sent to programs and many of them kill the program by default. Again, it depends on how the program is written to handle those signals. Signals can be sent using the kill command. "kill -l" lists all 64 signals.
+SIGHUP, number 1 on the list, stands for signal hang up. Hanging up on a stopped process results in the termination of that process. SIGINT, for Signal interrupt, is what is sent out when one presses the control c key. SIGILL generally gets sent out in the event of an illegal operation being performed. SIGTRAP is similar to SIGINT. SIGKILL is the agent 47 of kill signals. It never fails. SIGSTOP sends a stop signal to programs and when followed with a SIGCONTINUE effectively backgrounds the program. SIGSEGV is the signal sent out to kill programs that are seg faulting.
+===Scripting===
+Typing commands into the command line and watching the computer do your work for you while you laugh maniacally and pet your cat is all well and good, but isn't there sometimes even more efficient ways to implement your evil plans? The answer is "yes, scripting". A script is a series of shell commands that are organized in a document so that they can be fed automatically into the computer instead of manually typing them. Scripts start with #! in order to tell the computer which shell the script is written for as different shells have different languages associated with them. Typing "#! /bin/bash" tells the computer that the document is a bash script. Scripts aren't really programs and a script language isn't really a programming language. It's more like pseudo code. For example, while there are variables in bash, there are no variable types or memory allocation functions. All variables are basically treated as a string.
+There are some trick that Matt taught us about scripting. Curly braces isolate variable names in situations where the computer may misunderstand whether you are referring to a variable or the string you assigned to the variable name. Bash isn't really meant to complex calculations but it does have a command called "bc" which handles mathematical operations of some reasonable complexity. Some cool things you can do in bc is change the base used in calculations and change the output type to long int for more accuracy. Square brackets can be used to compare values. For example in the following code
+<code>
+["${result}" -eq "4"];
+</code>
+compares the value of the "result" variable to the number 4 and returns true if they are equal. The square brackets can be combined with if then statements in the usual programming way in order to give your scripts some decision making capabilities. The bash scripitng language also has for in loops which are analogous to for each loops in other programming languages such as C/C++. The following code snippet results in bash outputting the numbers 1-10 in standard output through the use of a for loop.
+<code>
+for ((x=0;$x<10;x++)); do
+      echo "x is $x"
+done
+</code>
+It's generally considered good practice to end scripts with an exit 0 command.
+===HTML===
+This week's project involved the use of HTML to create web pages and as a result was my first use of HTML. I learned a lot in the short time that I used it. HTML is used to toggle various properties of web pages (font of text, buttons, images) on and off. HTML works with tags that are placed around the object you want to toggle the property of. For example the <font></font> tags will change the font of the text within those tags. By the way, tags pretty much always start with <tag> and end with </tag>.
+I also ran into CSS, which is a product of the modern internet that people use within HTML code to gain further functionality and organization. For example with out the css command "style" I'm pretty sure it's impossible to customize your own button without creating an image of it and putting it on the page through the use of the <img> tag. I wasn't able to spend a lot of time in HTML and the code I created wasn't very intelligently written partly due to my ignorance but I look forward to having more opportunities to learn about it.
 ====MONTH Day, YEAR====
 This is a sample format for a dated entry. Please substitute the actual date for "Month Day, Year", and duplicate the level 4 heading to make additional entries.
 As an aid, feel free to use the following questions to help you generate content for your entries:
@@ Line 156: / Line 188: @@
   * What concepts are you dealing with that may not make perfect sense?
   * What challenges are you facing with respect to the course?

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