Changes

There are a few "classic problems" that students can encounter with their virtual machines and their host machine after performing lab2. Although all OPS235 OPS245 students may not encounter these problems, it is good to be aware of what a potential problem may look like, and know how to solve that problem.

{{Admon/tip|Bash Shell Scripting Tips:|<br>'''<u>The Here Document</u>'''<br><ul><li>A neat little trick involving a special type of redirection of stdin symbol: '''&lt;&lt;''' that allows input to be redirected to a command from within the command.<br><br> </li><li>Examples:<br><br>''cat &lt;&lt;+<br>This is a test message<br>This is the second line<br>+''<br><br>''mail -s "test message" youremailaddr &lt;&lt;+<br>This is a test message<br>I hope you like it.''<br>+<br><br>''tr [a-z] [A-Z] &lt;&lt;+<br>i like ops235<br>i love scripting.<br>+''<br><br></li></ul>'''<u>Using sed to Manipulate Text</u>'''<ul><li>The Linux command '''sed''' stands for <u>'''S'''</u>treaming <u>'''Ed'''</u>itor which is an effective way to manipulate a text file, output sent from a command, or from within a "here document". This command can manipulate matching text on a variety of criteria (such as '''line number(s)''', '''regular expression match''', etc). Commands can then be used for manipulation such as '''omitting''', '''printing''', '''substituting''', '''adding''', and '''inserting''' text.<br><br></li><li>The sed option '''-n''' suppresses display of text so the print ('''p''') command can be used; otherwise, the text will be displayed (with edits via the sed command instructions).<br><br></li><li>Results of text manipulation with sed can be stored in a variable using command substitution, or redirected to a file. '''NEVER redirect the stdout from a sed command to the same input file (or the input file will be destroyed)!''' <br><br></li><li>Examples<br><br>''sed 's/&#124;/ /g' &lt;&lt;+<br>I&#124;like&#124;weekends!<br>+''<br><br>''sed 's/$/\n/g' &lt;&lt;+<br>This text<br>should be<br>double-spaced!''<br>+<br><br></li></ul>}}

===Part 3: Generating Sofware Package Information with Shell ScriptsUsing sed to Filter Output from Commands===We will continue with using shell scripts commands to create a Software Information Report that manipulates output generated by the '''rpm''' command. The '''sed''' and '''awk''' commands are very useful tools in shell scripting to manipulate text. In this lab, we will be using ''sed'' to allow the user to select certain portions from the rpm command (options -qi).

rpm -qi $1 | sed -r -n "xchat</^($processedChoice)/ p" &gt;&gt; /root/package-info.txt<brcode><br>cat &lt;&lt;+<br/>File "/root/packageNotice that using the -i option with -infoq causes rpm to generate more output than we have seen from it so far.txt" has been created<br/li>+<brli>Pick any five packages and run the </code> rpm -qi<ol/code><li value="8">Save, set permissions, and then run that shell script for command on all five at once. This should produce dozens of lines of output. Consider the application '''gedit'''. Did output it create that report? Try running the script without an argument would generate if we used - What did it do? a instead of picking just a few packages.<li>Use the <bli>Run <code>wgetrpm -qia</code>now.)</bli> command <li>That is way too much output for us to downloadreasonably search through, study, and run the following shell scripts on-line:but we have commands that can filter this down to a much more readable amount.<blockquote/li><bli>Try the command: <code><span style=" pointerrpm -qia | sed -eventsnre '/^Name&#91;&#91;:nonespace:&#93;&#93;cursor+:default/ p' -e '/^Install Date&#91;&#91;color:space:&#3366CC93;font-size:1.2em&#93;">https*://ict.senecacollege.ca/~ops245/labs/packageInfoGraphical.bash</span>p'</code><br /b></blockquote>Instead of printing every line, this will only display the name and install date of each package.</li><li>Try modifying that command to understand what this Bash Shell script doesdisplay only the package name and License.</li></ol>

Now that we have added some powerful logical structures to our python scripts, we can make our scripts much more adaptable. Just like we have done in bash, our Our python scripts can now respond to different situations by executing different code, or repeating the same code several times (e.g. keep asking the user for input until they give us something useful). In this investigation you will write a python script that will prompt a user for a directory to archive, ask them if they want the archive compressed, and (only if they do want compression) what type of compression to apply.