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  13.         Lab 5: Bash scripting - HackMD

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  37.     <div id="doc" class="markdown-body container-fluid comment-enabled" data-hard-breaks="true"><h1 id="Lab-5-Bash-scripting" data-id="Lab-5-Bash-scripting"><a class="anchor hidden-xs" href="#Lab-5-Bash-scripting" title="Lab-5-Bash-scripting"><span class="octicon octicon-link"></span></a><span>Lab 5: Bash scripting</span></h1><h2 id="Exercise-1---Bash-basics" data-id="Exercise-1---Bash-basics"><a class="anchor hidden-xs" href="#Exercise-1---Bash-basics" title="Exercise-1---Bash-basics"><span class="octicon octicon-link"></span></a><span>Exercise 1 - Bash basics</span></h2><h3 id="Task-1---Bash-scripting-basics" data-id="Task-1---Bash-scripting-basics"><a class="anchor hidden-xs" href="#Task-1---Bash-scripting-basics" title="Task-1---Bash-scripting-basics"><span class="octicon octicon-link"></span></a><span>Task 1 - Bash scripting basics</span></h3><ul>

  38. <li><span>Use the </span><code>echo</code><span> command to display a line of text. echo has three important options </span><code>-n</code><span>, </span><code>-e</code><span>, and </span><code>-E</code><span>. Read the echo manual.</span><br>

  39. <span>Create a shell script </span><code>lab_5.sh</code><span> and add the following to see the output when you use the various echo options.</span><pre><code>#!/bin/bash

  40. echo -E "Printing text with newline. This is the default option."

  41. echo -n "What happens when we print text without new line"

  42. echo -e "\nEscaping \t characters \t to print\nnew lines for example"

  43. </code></pre>

  44. <span>Execute the script.</span><pre><code>$ bash lab_5.sh

  45. </code></pre>

  46. </li>

  47. <li><span>Single line comments begin with </span><code>#</code><span>. Append the following lines to </span><code>lab_5.sh</code><span>.</span><pre><code># Adding comments that do nothing

  48. echo "Testing single line comments"

  49. </code></pre>

  50. <span>Execute the script to see what happens.</span></li>

  51. <li><span>You can use multi line comments. The format is to start with a colon </span><code>:</code><span> followed by the comments enclosed in single quotes </span><code>'</code><span>. For example, append the following to </span><code>lab_5.sh</code><span>.</span><pre><code>: '

  52. This is a multi line comment

  53. Nothing happens in this section

  54. '

  55. echo "Back to executable commands"

  56. </code></pre>

  57. <span>Execute the script to see what happens.</span></li>

  58. <li><span>Double brackets are used to do arithmetic tasks. For example, append the following to </span><code>lab_5.sh</code><pre><code># Add two numeric values

  59. ((sum = 12 + 24))

  60. 

  61. # Print the sum

  62. echo $sum

  63. </code></pre>

  64. </li>

  65. <li><span>Get user input with the </span><code>read</code><span> command. This is normally used in combination with echo to print a prompt to the user. Append the following to </span><code>lab_5.sh</code><span>.</span><pre><code>echo "What is your favorite fruit?"

  66. read fruit

  67. echo "Hey! I like $fruit too."

  68. </code></pre>

  69. </li>

  70. </ul><h3 id="Task-2---Bash-loops-and-conditions" data-id="Task-2---Bash-loops-and-conditions"><a class="anchor hidden-xs" href="#Task-2---Bash-loops-and-conditions" title="Task-2---Bash-loops-and-conditions"><span class="octicon octicon-link"></span></a><span>Task 2 - Bash loops and conditions</span></h3><ul>

  71. <li>

  72. <p><span>Create a simple </span><strong><span>while</span></strong><span> loop. Save the following script as </span><code>while_loop.sh</code><span>.</span></p>

  73. <pre><code>#!/bin/bash

  74. 

  75. counter=1

  76. while [ $counter -le 10 ]

  77. do

  78.   echo $counter

  79.   ((counter++))

  80. done

  81. echo All done

  82. </code></pre>

  83. <blockquote>

  84. <p><code>-le</code><span> is the same as </span><code>&lt;=</code><span>.</span></p>

  85. </blockquote>

  86. </li>

  87. <li>

  88. <p><span>Create an </span><strong><span>until</span></strong><span> loop. The until loop will execute the commands within it until the condition becomes true. Save the following script as </span><code>until_loop.sh</code><span>.</span></p>

  89. <pre><code>#!/bin/bash

  90. 

  91. counter=1

  92. until [ $counter -gt 10 ]

  93. do

  94.   echo $counter

  95.   ((counter++))

  96. done

  97. echo All done

  98. </code></pre>

  99. <blockquote>

  100. <p><code>-gt</code><span> is the same as </span><code>&gt;</code><span>.</span></p>

  101. </blockquote>

  102. </li>

  103. <li>

  104. <p><span>Create a simple </span><strong><span>for</span></strong><span> loop that iterates through the item in a list and prints each of them. Save the following script as </span><code>for_loop.sh</code><span>.</span></p>

  105. <pre><code>#!/bin/bash

  106. 

  107. names='Liliya Peter Emili'

  108. for name in $names

  109. do

  110.   echo $name

  111. done

  112. echo All done

  113. </code></pre>

  114. </li>

  115. <li>

  116. <p><span>Bash </span><code>for</code><span> loop can be written in “C-Style”. For example save the following script as </span><code>uptime.sh</code><span>.</span></p>

  117. <pre><code>#!/bin/bash

  118. 

  119. # Loop of ten iterations to print system uptime every 2 seconds.

  120. for ((i = 1 ; i &lt;= 10 ; i++)); do

  121.   

  122.   echo -e "$i.\t"$(uptime)

  123.   sleep 2

  124. done

  125. </code></pre>

  126. <p><span>Execute the script and analyze the output.</span></p>

  127. </li>

  128. <li>

  129. <p><span>The </span><strong><span>break</span></strong><span> statement tells bash to exit the loop. An example is shown in </span><code>break.sh</code><span> below.</span></p>

  130. <pre><code>#!/bin/bash

  131. 

  132. counter=1

  133. while [ $counter -le 10 ]

  134. do

  135.   if [ $counter -eq 5 ]

  136.   then

  137.     echo Script encountered the value $counter

  138.     break

  139.   fi

  140.   echo $counter

  141.   ((counter++))

  142. done

  143. echo All done

  144. </code></pre>

  145. <blockquote>

  146. <p><code>-eq</code><span> is the same as </span><code>==</code><span>.</span></p>

  147. </blockquote>

  148. </li>

  149. <li>

  150. <p><span>The </span><strong><span>continue</span></strong><span> statement skips the cuttent iteration of the loop. Save the following as </span><code>continue.sh</code><span> and run it.</span></p>

  151. <pre><code>#!/bin/bash

  152. 

  153. counter=0

  154. while [ $counter -lt 10 ]

  155. do

  156.   ((counter++))

  157.   if [ $counter -eq 6 ]

  158.   then

  159.     echo Number 6 encountered, skipping to the next iteration

  160.     continue

  161.   fi

  162.   echo $counter

  163. done

  164. echo All done

  165. </code></pre>

  166. <blockquote>

  167. <p><code>-lt</code><span> is the same as </span><code>&lt;</code><span>.</span></p>

  168. </blockquote>

  169. </li>

  170. </ul><h3 id="Task-3---If-statements" data-id="Task-3---If-statements"><a class="anchor hidden-xs" href="#Task-3---If-statements" title="Task-3---If-statements"><span class="octicon octicon-link"></span></a><span>Task 3 - If statements</span></h3><ul>

  171. <li>

  172. <p><span>If statements allow us to make decisions in our script. This is usually utilized with a comparison operator. Save the following as </span><code>if_statement.sh</code><span>.</span></p>

  173. <pre><code>#!/bin/bash

  174. 

  175. echo -n "Enter the number: "

  176. read number

  177. if [ $number -gt 100 ]

  178. then

  179.   echo That\'s a large number.

  180. elif [ $number -gt 50 ]

  181. then

  182.   echo Not so much.

  183. else

  184.   echo The number is way too small.

  185. fi

  186. </code></pre>

  187. </li>

  188. </ul><h3 id="Task-4---Bash-functions" data-id="Task-4---Bash-functions"><a class="anchor hidden-xs" href="#Task-4---Bash-functions" title="Task-4---Bash-functions"><span class="octicon octicon-link"></span></a><span>Task 4 - Bash functions</span></h3><ul>

  189. <li>

  190. <p><span>Create a simple function</span></p>

  191. <pre><code>$ fun () { echo "This is a function"; echo; }

  192. </code></pre>

  193. </li>

  194. <li>

  195. <p><span>To view the content of all functions defined in the shell</span></p>

  196. <pre><code>$ declare -f

  197. </code></pre>

  198. </li>

  199. <li>

  200. <p><span>To list all functions by its name</span></p>

  201. <pre><code>$ declare -F

  202. </code></pre>

  203. </li>

  204. <li>

  205. <p><span>To view the content of the one your function</span></p>

  206. <pre><code>$ declare -f fun

  207. </code></pre>

  208. </li>

  209. <li>

  210. <p><span>To remove the function</span></p>

  211. <pre><code>$ unset fun

  212. </code></pre>

  213. </li>

  214. <li>

  215. <p><span>Now lets create a script with a 2 functions inside it</span></p>

  216. <pre><code>$ vim funky.sh

  217. </code></pre>

  218. </li>

  219. <li>

  220. <p><span>Inside vim type the following</span></p>

  221. <pre><code>#!/bin/bash

  222. 

  223. JUST_A_SECOND=3

  224. funky ()

  225. { # This is about as simple as functions get.

  226. 

  227.     echo "This is a funky function."

  228.     echo "Now exiting funky function."

  229. } # Function declaration must precede call

  230. 

  231. fun ()

  232. { # A somewhat more complex function. 

  233.     i=0

  234.     REPEATS=30

  235.     echo

  236.     echo "And now the fun really begins."

  237.     echo 

  238.     sleep $JUST_A_SECOND 

  239.     while [ $i -lt $REPEATS ] #use as (&lt;,&gt;,=) or (-lt, -gt, -eq)

  240.         do

  241.         echo   "----------FUNCTIONS----------&gt;"

  242.         echo   "&lt;------------ARE-------------"

  243.         echo   "&lt;------------FUN------------&gt;"

  244.         echo

  245.         let "i+=1"

  246.         done

  247. }

  248. 

  249. add_fun()

  250. {

  251. # A function just to add numbers

  252. echo $((2+2))

  253. }

  254. #Now, call the functions

  255. funky

  256. fun

  257. echo The return value of add_fun is: $(add_fun)

  258. echo exit $? #check your exit status of the last function/command: if 0-success, otherwise is not

  259. </code></pre>

  260. </li>

  261. <li>

  262. <p><span>Run the script</span></p>

  263. <pre><code>$ bash funky.sh

  264. </code></pre>

  265. </li>

  266. <li>

  267. <p><span>Notice how the functions are only available within the one shell (once you exit it is gone for the parent shell)</span></p>

  268. <pre><code>$ declare -F

  269. </code></pre>

  270. </li>

  271. </ul><h2 id="Exercise-2---Working-with-files-and-directories" data-id="Exercise-2---Working-with-files-and-directories"><a class="anchor hidden-xs" href="#Exercise-2---Working-with-files-and-directories" title="Exercise-2---Working-with-files-and-directories"><span class="octicon octicon-link"></span></a><span>Exercise 2 - Working with files and directories</span></h2><h3 id="Task-1---File-and-directory-test-operators" data-id="Task-1---File-and-directory-test-operators"><a class="anchor hidden-xs" href="#Task-1---File-and-directory-test-operators" title="Task-1---File-and-directory-test-operators"><span class="octicon octicon-link"></span></a><span>Task 1 - File and directory test operators</span></h3><p><span>There are several options in bash to check the type of file you are interacting with. In many cases, the options are also used to check for the existence of a specified file or directory. The example below shows the options that can be used.</span></p><ul>

  272. <li><span>Create a script </span><code>file_checker.sh</code><span> and add the following code:</span><pre><code>#!/bin/bash

  273. 

  274. if [[ $# -le 0 ]]

  275. then

  276.   echo "You did not pass any files as arguments to the script."

  277.   echo "Usage:" "$0" "my-file-1 my-file-2"

  278.   exit

  279. fi

  280. 

  281. for arg in "$@"

  282. do

  283.   # Does it actually exist?

  284.   if [[ ! -e "$arg" ]]

  285.   then

  286.       echo "* Skipping ${arg}"

  287.       continue

  288.   fi

  289. 

  290.   # Is it a regular file?

  291.   if [ -f "$arg" ]

  292.   then

  293.       echo "* $arg is a regular file!"

  294.   else

  295.       echo "* $arg is not a regular file!"

  296.   fi

  297. 

  298.   [ -b "$arg" ] &amp;&amp; echo "* $arg is a block device."

  299.   [ -d "$arg" ] &amp;&amp; echo "* $arg is a directory."

  300.   [ ! -d "$arg" ] &amp;&amp; echo "* $arg is not a directory."

  301. 

  302.   [ -x "$arg" ] &amp;&amp; echo "* $arg is executable."

  303.   [ ! -x "$arg" ] &amp;&amp; echo "* $arg is not executable."

  304. 

  305.   [[ -h "$arg" ]] &amp;&amp; echo "* $arg is a symbolic link."

  306.   [ ! -h "$arg" ] &amp;&amp; echo "* $arg is not a symbolic link."

  307. 

  308.   [[ -s "$arg" ]] &amp;&amp; echo "* $arg has nonzero size."

  309.   [ ! -s "$arg" ] &amp;&amp; echo "* $arg has zero size."

  310. 

  311.   [[ -r "$arg" &amp;&amp; -d "$arg" ]] &amp;&amp; echo "* $arg is a readable directory."

  312.   [[ -r "$arg" &amp;&amp; -f "$arg" ]] &amp;&amp; echo "* $arg is a readable regular file."

  313. done

  314. </code></pre>

  315. </li>

  316. <li><span>Run the script and specify the files you want to check as arguments.</span><pre><code># bash file_checker.sh /bin/i386 /etc/passwd

  317. </code></pre>

  318. <span>You should get output similar to the following:</span><pre><code>* /bin/i386 is a regular file!

  319. * /bin/i386 is not a directory.

  320. * /bin/i386 is executable.

  321. * /bin/i386 is a symbolic link.

  322. * /bin/i386 has nonzero size.

  323. * /bin/i386 is a readable regular file.

  324. * /etc/passwd is a regular file!

  325. * /etc/passwd is not a directory.

  326. * /etc/passwd is not executable.

  327. * /etc/passwd is not a symbolic link.

  328. * /etc/passwd has nonzero size.

  329. * /etc/passwd is a readable regular file.

  330. </code></pre>

  331. </li>

  332. </ul><h3 id="Task-2---Directory-and-file-manipulation" data-id="Task-2---Directory-and-file-manipulation"><a class="anchor hidden-xs" href="#Task-2---Directory-and-file-manipulation" title="Task-2---Directory-and-file-manipulation"><span class="octicon octicon-link"></span></a><span>Task 2 - Directory and file manipulation</span></h3><ul>

  333. <li>

  334. <p><span>You can create a new directory in bash with the </span><code>mkdir</code><span> command. Save the following script as </span><code>mkdir_bash.sh</code><span>.</span></p>

  335. <pre><code>#!/bin/bash

  336. echo "Enter directory name"

  337. read newdir

  338. `mkdir $newdir`

  339. </code></pre>

  340. </li>

  341. <li>

  342. <p><span>You can check for the existence of a directory before proceeding to create it. Update </span><code>mkdir_bash.sh</code><span> to look like the script shown below.</span></p>

  343. <pre><code>#!/bin/bash

  344. echo "Enter directory name"

  345. read newdir

  346. if [ -d "$newdir" ]

  347. then

  348.   echo "Directory exist"

  349. else

  350.   `mkdir $newdir`

  351.   echo "Directory created"

  352. fi

  353. </code></pre>

  354. </li>

  355. <li>

  356. <p><span>Create a bash script to read every line of a specified file. The file name is passed as a command line argument. Save the following script as </span><code>file_reader.sh</code><span>.</span></p>

  357. <pre><code>#!/bin/bash

  358. 

  359. file=$1

  360. 

  361. if [[ "$file" == "" || (! -f "$file") ]]

  362. then

  363.   echo Using standard input!

  364.   file="/dev/stdin"

  365. fi

  366. 

  367. while read -r line

  368. do

  369.   echo "$line"

  370. done &lt; "${file}"

  371. </code></pre>

  372. <blockquote>

  373. <p><span>The script reads the first value passed as a command line argument, represented by $1. If a text file is passed, the script will read and output each line of text.</span><br>

  374. <span>If no command line argument is passed or if the file does not exist, standard input (/dev/stdin) is used instead. This will prompt you to enter text and will output to the terminal screen what is received as input. To signal the end of your stdin input type CTRL+D</span></p>

  375. </blockquote>

  376. <p><span>Use this script to read </span><code>/etc/passwd</code><span>.</span></p>

  377. <pre><code>$ bash file_reader.sh /etc/passwd

  378. </code></pre>

  379. </li>

  380. <li>

  381. <p><span>The Internal Field Separator (IFS) is used to recognize word boundaries. The default value for IFS consists of whitespace characters. Whitespace characters are space, tab and newline. Add the following script to the file </span><code>ifs_test.sh</code><span>.</span></p>

  382. <pre><code>#!/bin/bash

  383. 

  384. mystring="foo:bar baz rab"

  385. for word in $mystring; do

  386.   echo "Word: $word"

  387. done

  388. </code></pre>

  389. <p><span>Run the script.</span></p>

  390. </li>

  391. <li>

  392. <p><span>The default value for the IFS can be changed. Modify </span><code>ifs_test.sh</code><span> to contain the following.</span></p>

  393. <pre><code>#!/bin/bash

  394. 

  395. IFS=:

  396. mystring="foo:bar baz rab"

  397. for word in $mystring; do

  398.   echo "Word: $word"

  399. done

  400. </code></pre>

  401. </li>

  402. <li>

  403. <p><span>Let’s do this on a larger scale. Read /etc/passwd word by word while using </span><code>:</code><span> as the IFS. Save the following as </span><code>ifs_word.sh</code><span>.</span></p>

  404. <pre><code>#!/bin/bash

  405. 

  406. if [[ $# -le 0 ]]

  407. then

  408.   echo "You did not pass any files as arguments to the script."

  409.   echo "Usage:" "$0" "my-file"

  410.   exit

  411. fi

  412. 

  413. IFS=:

  414. file=$1

  415. 

  416. if [ ! -f "$file" ]

  417. then

  418.   echo "File does not exist!"

  419. fi

  420. 

  421. for word in $(cat "${file}")

  422. do

  423.   echo "$word"

  424. done

  425. </code></pre>

  426. <p><span>Run the script specifying </span><code>/etc/passwd</code><span> as an argument.</span></p>

  427. <pre><code>$ bash ifs_word.sh /etc/passwd

  428. </code></pre>

  429. </li>

  430. </ul><h3 id="Task-3---Jump-directories" data-id="Task-3---Jump-directories"><a class="anchor hidden-xs" href="#Task-3---Jump-directories" title="Task-3---Jump-directories"><span class="octicon octicon-link"></span></a><span>Task 3 - Jump directories</span></h3><p><span>Sometimes it is difficult to navigate directories with the possibly infinite number of parent directories we need to provide. For example </span><code>cd ../../../../../</code><span>. Let’s create a script that will help us jump to a specified directory without executing </span><code>cd ../</code><span>.</span></p><ul>

  431. <li><span>Create the script </span><code>jump_dir.sh</code><span>.</span><pre><code># !/bin/bash

  432. 

  433. # A simple bash script to move up to desired directory level directly

  434. 

  435. function jump()

  436. {

  437.   # original value of Internal Field Separator

  438.   OLDIFS=$IFS

  439. 

  440.   # setting field separator to "/"

  441.   IFS=/

  442. 

  443.   # converting working path into array of directories in path

  444.   # eg. /my/path/is/like/this

  445.   # into [, my, path, is, like, this]

  446.   path_arr=($PWD)

  447. 

  448.   # setting IFS to original value

  449.   IFS=$OLDIFS

  450. 

  451.   local pos=-1

  452. 

  453.   # ${path_arr[@]} gives all the values in path_arr

  454.   for dir in "${path_arr[@]}"

  455.   do

  456.     # find the number of directories to move up to

  457.     # reach at target directory

  458.     pos=$[$pos+1]

  459.     if [ "$1" = "$dir" ];then

  460. 

  461.   	# length of the path_arr

  462.   	dir_in_path=${#path_arr[@]}

  463. 

  464.   	#current working directory

  465.   	cwd=$PWD

  466.   	limit=$[$dir_in_path-$pos-1]

  467.   	for ((i=0; i&lt;limit; i++))

  468.   	do

  469.   	  cwd=$cwd/..

  470.   	done

  471.   	cd $cwd

  472.       break

  473.     fi

  474.   done

  475. }

  476. </code></pre>

  477. </li>

  478. <li><span>Make the script executable</span><pre><code>$ chmod +x jump_dir.sh

  479. </code></pre>

  480. </li>

  481. <li><span>Add it to the .bashrc file to make it available on every terminal session.</span><pre><code>echo "source ~/jump_dir.sh"&gt;&gt; ~/.bashrc

  482. </code></pre>

  483. </li>

  484. <li><span>Open a new terminal and try jumping.</span><pre><code>$ jump directory_name

  485. </code></pre>

  486. </li>

  487. </ul><h2 id="Exercise-3---Hash-tables-and-more-bash-usage" data-id="Exercise-3---Hash-tables-and-more-bash-usage"><a class="anchor hidden-xs" href="#Exercise-3---Hash-tables-and-more-bash-usage" title="Exercise-3---Hash-tables-and-more-bash-usage"><span class="octicon octicon-link"></span></a><span>Exercise 3 - Hash tables and more bash usage</span></h2><h3 id="Task-1---Hash-tables-in-bash" data-id="Task-1---Hash-tables-in-bash"><a class="anchor hidden-xs" href="#Task-1---Hash-tables-in-bash" title="Task-1---Hash-tables-in-bash"><span class="octicon octicon-link"></span></a><span>Task 1 - Hash tables in bash</span></h3><p><span>A dictionary, or a hashmap, or an associative array is a data structure used to store a collection of things. A dictionary consists of a collection of key-value pairs. Each key is mapped to its associated value.</span></p><ul>

  488. <li><span>To declare a dictionary variable in bash, use the </span><code>declare</code><span> statement with the </span><code>-A</code><span> option which means associative array. For example:</span><pre><code>$ declare -A newDictionary

  489. </code></pre>

  490. </li>

  491. <li><span>We have declared a variable called </span><code>newDictionary</code><span>. The following syntax can be used to add key-value pairs to the dictionary:</span><pre><code>$ newDictionary[key]=value

  492. </code></pre>

  493. </li>

  494. <li><span>Let’s add a key-value pair to the dictionary using the syntax above:</span><pre><code>$ newDictionary[1]=SNA

  495. $ newDictionary[2]=IML

  496. </code></pre>

  497. </li>

  498. <li><span>To retrive the value of a dictionary key, we have to add </span><code>$</code><span> with braces </span><code>{}</code><span> to the dictionary variable we defined.</span><pre><code>$ echo ${newDictionary[1]}

  499. </code></pre>

  500. </li>

  501. <li><span>To update the value of a key, we simply overwrite the existing value by writing to the key again. For example, to update </span><code>newDictionary[1]</code><span>, we do the following:</span><pre><code>$ newDictionary[1]=NEWSNA

  502. </code></pre>

  503. <span>Retrieve the value of they key </span><code>[1]</code><span> to verify the update.</span><pre><code>$ echo ${newDictionary[1]}

  504. NEWSNA

  505. </code></pre>

  506. </li>

  507. <li><span>Use the </span><code>unset</code><span> command to remove a key-value pair from the dictionary.</span><pre><code>$ unset newDictionary[1]

  508. </code></pre>

  509. <span>Verify that the pair has been removed from the dictionary.</span><pre><code>$ echo ${newDictionary[1]}

  510. </code></pre>

  511. </li>

  512. <li><span>You can iterate through the dictionary by creating a </span><code>for</code><span> loop. An example is shown in the script below:</span><pre><code>#!/bin/bash

  513. declare -A newDictionary

  514. newDictionary[1]=SNA

  515. newDictionary[2]=IML

  516. newDictionary[3]=SSN

  517. for key in "${!newDictionary[@]}"; do 

  518.   echo "$key ${newDictionary[$key]}" 

  519. done

  520. </code></pre>

  521. <span>You should get an output similar to the following when you run the script:</span><pre><code>3 SSN

  522. 2 IML

  523. 1 SNA

  524. </code></pre>

  525. </li>

  526. <li><span>You can also declare and instantiate a dictionary in one line.</span><pre><code>$ declare -A innoCourses=([1]=SNA [2]=IML [3]=SSN)

  527. </code></pre>

  528. <span>Check the content of the dictionary.</span><pre><code>echo ${innoCourses[3]}

  529. </code></pre>

  530. </li>

  531. </ul><h3 id="Task-2---Use-sed-in-bash" data-id="Task-2---Use-sed-in-bash"><a class="anchor hidden-xs" href="#Task-2---Use-sed-in-bash" title="Task-2---Use-sed-in-bash"><span class="octicon octicon-link"></span></a><span>Task 2 - Use sed in bash</span></h3><ul>

  532. <li><span>Use sed to strip all HTML tags in a HTML page. Save the following code as </span><code>sed_bash.sh</code><span>.</span><pre><code>#!/bin/bash

  533. 

  534. strip-tags ()

  535. {

  536.   sed -e 's/&lt;[^&gt;]*.//g' -

  537. }

  538. curl https://example.com/ --silent | strip-tags

  539. </code></pre>

  540. <span>Run the bash script and analyse the output. There is no HTML tag in the results.</span></li>

  541. </ul><h3 id="Task-3---Execute-Python-commands-in-bash" data-id="Task-3---Execute-Python-commands-in-bash"><a class="anchor hidden-xs" href="#Task-3---Execute-Python-commands-in-bash" title="Task-3---Execute-Python-commands-in-bash"><span class="octicon octicon-link"></span></a><span>Task 3 - Execute Python commands in bash</span></h3><ul>

  542. <li><span>Python can run one-liners from an operating system command line using option </span><code>-c</code><span>. An example is shown with the command below:</span><pre><code>$ python3 -c "a = 2; b = 4; sum = a + b; print('Sum =', sum)"

  543. or

  544. $ python -c "a = 2; b = 4; sum = a + b; print('Sum =', sum)"

  545. </code></pre>

  546. <span>The following bash script executes the python command above.</span><pre><code>#!/bin/bash

  547. 

  548. python3 -c "a = 2; b = 4; sum = a + b; print('Sum =', sum)"

  549. </code></pre>

  550. </li>

  551. <li><span>Alternatively, you scan split your python code into multi-lines by declaring a variable in the following fashion:</span><pre><code>#!/bin/bash

  552. 

  553. py_script="

  554. a = 2

  555. b = 4

  556. sum = a + b

  557. print('Sum =', sum)

  558. "

  559. 

  560. python3 -c "$py_script"

  561. </code></pre>

  562. </li>

  563. </ul><h2 id="Exercise-4---Debugging-bash-scripts" data-id="Exercise-4---Debugging-bash-scripts"><a class="anchor hidden-xs" href="#Exercise-4---Debugging-bash-scripts" title="Exercise-4---Debugging-bash-scripts"><span class="octicon octicon-link"></span></a><span>Exercise 4 - Debugging bash scripts</span></h2><h3 id="Task-1---Command-exit-code" data-id="Task-1---Command-exit-code"><a class="anchor hidden-xs" href="#Task-1---Command-exit-code" title="Task-1---Command-exit-code"><span class="octicon octicon-link"></span></a><span>Task 1 - Command exit code</span></h3><p><span>You can verify whether a bash command executed successfully by viewing the exit status code of the command. The exit status of the previously executed command is stored in the </span><code>$?</code><span> variable. A successful command returns a </span><code>0</code><span>, while an unsuccessful one returns a non-zero value that usually can be interpreted as an error code.</span></p><ul>

  564. <li><span>Run the command </span><code>$ ls -lah</code><span>.</span></li>

  565. <li><span>View the exit status of the previous command with </span><code>$ echo "$?"</code><span>.</span></li>

  566. <li><span>Now run a command that will fail. For example: </span><code>$ ls -lah /directorythatdoesnotexist</code></li>

  567. <li><span>Run </span><code>$ echo "$?"</code><span> again to view the exit status. You should get a value that is not </span><code>0</code><span>.</span></li>

  568. </ul><h3 id="Task-2---Using-set--xe" data-id="Task-2---Using-set--xe"><a class="anchor hidden-xs" href="#Task-2---Using-set--xe" title="Task-2---Using-set--xe"><span class="octicon octicon-link"></span></a><span>Task 2 - Using </span><code>set -xe</code></h3><p><span>When there is an error that stops the execution of a bash script, the bash interpreter usually displays the line number that triggered the error. However, in some cases, it might be necessary to trace the flow of execution of the script. This provides more insight into the conditions that are met, and the state of the loops.</span></p><ul>

  569. <li><span>The </span><code>set</code><span> command is used to set or unset shell options or positional parameters.</span></li>

  570. <li><span>We can use the </span><code>set -e</code><span> option to exit the bash script if any command or statement generates a non-zero exit code. This is defined at the start of the script and it applies globally to all commands in the script.</span></li>

  571. <li><span>Additionally, we can also use the </span><code>set -x</code><span> option to display commands and arguments before they are executed. With this option, we can see every line of command that is executing in the script.</span></li>

  572. <li><span>The </span><code>set -e</code><span> option and </span><code>-x</code><span> options can be combined to become useful debugging tools. The option </span><code>-e</code><span> exits the script as soon as an error is encountered, and the option </span><code>-x</code><span> shows the command that was running when the error was encountered.</span></li>

  573. <li><span>Create a bash script </span><code>loop_debug.sh</code><span> and add the following to it:</span><pre><code>#!/bin/bash

  574. 

  575. set -xe

  576. 

  577. # This script prints all user profiles.

  578. 

  579. FILE=".bashrc"  #  File containing user profile,

  580.             #+ was ".profile" in original script.

  581. 

  582. for home in `awk -F: '{print $6}' /etc/passwd`

  583. do

  584.   [ -d "$home" ] || continue    # If no home directory, go to next.

  585.   [ -r "$home" ] || continue    # If not readable, go to next.

  586.   (cd $home; [ -e $FILE ] &amp;&amp; less $FILE)

  587. done

  588. 

  589. exit 0

  590. </code></pre>

  591. </li>

  592. <li><span>Run the script and analyze the output. Did the script stop prematurely?</span></li>

  593. <li><span>Remove the option </span><code>-e</code><span> and run the script again. Did you notice any difference? Why is it different?</span></li>

  594. <li><span>Now completely remove </span><code>set -xe</code><span> to see how the program executes without these options.</span></li>

  595. </ul><h2 id="Questions-to-answer" data-id="Questions-to-answer"><a class="anchor hidden-xs" href="#Questions-to-answer" title="Questions-to-answer"><span class="octicon octicon-link"></span></a><span>Questions to answer</span></h2><blockquote>

  596. <ul>

  597. <li><span>Upload the shell script files to moodle.</span></li>

  598. <li><span>Test every feature in your script and show screenshots of the test in your report.</span></li>

  599. </ul>

  600. </blockquote><ol>

  601. <li>

  602. <p><span>Write a bash script that displays the following details of the logged-in user from the environment variables:</span></p>

  603. <ul>

  604. <li><span>Login username</span></li>

  605. <li><span>Home directory</span></li>

  606. <li><span>Shell</span></li>

  607. <li><span>The hostname of the system</span></li>

  608. <li><span>The script should extract the IP address of the system from the </span><code>ifconfig</code><span> or </span><code>ip</code><span> command. Save the IP address to the </span><code>ipaddress</code><span> variable and display it as output.</span></li>

  609. </ul>

  610. <p><span>Sample output:</span></p>

  611. <pre><code>Username: user1

  612. Home Directory: /home/user1

  613. Shell: /bin/bash

  614. Hostname: ubuntuvm

  615. IP address: 10.1.1.1

  616. </code></pre>

  617. </li>

  618. <li>

  619. <p><span>Backups are important in system administration. Create a script that will backup your home directory.</span></p>

  620. <ul>

  621. <li><span>The backup file should be compressed to </span><code>tar.gz</code><span>.</span></li>

  622. <li><span>All files and directory permissions should be preserved in the backup.</span></li>

  623. <li><span>The backup destination directory is </span><code>/var/backups/</code></li>

  624. <li><span>The script should create the destination directory if it doesn’t already exist.</span></li>

  625. <li><span>The backup file name should take the format </span><code>home_backup_month_day_year_hour_minute_second.tar.gz</code><span>.</span><br>

  626. <span>For example </span><code>home_backup_Feb_18_2023_02_30_02.tar.gz</code></li>

  627. </ul>

  628. <blockquote>

  629. <p><span>A typical real life scenario is keeping backups of websites. Administrators are usually interested in backing up </span><code>/var/www/html</code><span>.</span></p>

  630. </blockquote>

  631. </li>

  632. <li>

  633. <p><span>Write a bash script that checks various artifacts on the system. The script mainly checks for system information, and OS components. Your script should do the following:</span></p>

  634. <ul>

  635. <li><span>Print the OS kernel name and kernel version.</span></li>

  636. <li><span>Print the system architecture.</span></li>

  637. <li><span>Print all currently logged in users (show the date or time which the users logged in, and show the command line of the users’ current process).</span></li>

  638. <li><span>Verify that EFI is enabled and print the relevant output.</span></li>

  639. <li><span>List all connected block devices (</span><strong><span>Bonus:</span></strong><span> Identify the devices that have the GPT partition by adding an </span><code>*</code><span> to them in the output).</span></li>

  640. <li><span>List the first boot device on your system. This should be done according to the boot order in the NVRAM.</span></li>

  641. </ul>

  642. <blockquote>

  643. <p><span>Ensure that the output of your script is neatly formatted and easy to read.</span><br>

  644. <span>Bonus points if you create and use at least three functions.</span></p>

  645. </blockquote>

  646. </li>

  647. </ol><h3 id="Bonus" data-id="Bonus"><a class="anchor hidden-xs" href="#Bonus" title="Bonus"><span class="octicon octicon-link"></span></a><span>Bonus</span></h3><ol start="4">

  648. <li><span>Write a bash script that scans the entire system for files that contain the string “/bin/bash”. The script should print only the matches that the currently logged in user has execute permission on.</span></li>

  649. </ol></div>

  650.     <div class="ui-toc dropup unselectable hidden-print" style="display:none;">

  651.         <div class="pull-right dropdown">

  652.             <a id="tocLabel" class="ui-toc-label btn btn-default" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false" title="Table of content">

  653.                 <i class="fa fa-bars"></i>

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  655.             <ul id="ui-toc" class="ui-toc-dropdown dropdown-menu" aria-labelledby="tocLabel">

  656.                 <div class="toc"><ul class="nav">

  657. <li><a href="#Lab-5-Bash-scripting" title="Lab 5: Bash scripting">Lab 5: Bash scripting</a><ul class="nav">

  658. <li><a href="#Exercise-1---Bash-basics" title="Exercise 1 - Bash basics">Exercise 1 - Bash basics</a><ul class="nav">

  659. <li><a href="#Task-1---Bash-scripting-basics" title="Task 1 - Bash scripting basics">Task 1 - Bash scripting basics</a></li>

  660. <li><a href="#Task-2---Bash-loops-and-conditions" title="Task 2 - Bash loops and conditions">Task 2 - Bash loops and conditions</a></li>

  661. <li><a href="#Task-3---If-statements" title="Task 3 - If statements">Task 3 - If statements</a></li>

  662. <li><a href="#Task-4---Bash-functions" title="Task 4 - Bash functions">Task 4 - Bash functions</a></li>

  663. </ul>

  664. </li>

  665. <li><a href="#Exercise-2---Working-with-files-and-directories" title="Exercise 2 - Working with files and directories">Exercise 2 - Working with files and directories</a><ul class="nav">

  666. <li><a href="#Task-1---File-and-directory-test-operators" title="Task 1 - File and directory test operators">Task 1 - File and directory test operators</a></li>

  667. <li><a href="#Task-2---Directory-and-file-manipulation" title="Task 2 - Directory and file manipulation">Task 2 - Directory and file manipulation</a></li>

  668. <li><a href="#Task-3---Jump-directories" title="Task 3 - Jump directories">Task 3 - Jump directories</a></li>

  669. </ul>

  670. </li>

  671. <li><a href="#Exercise-3---Hash-tables-and-more-bash-usage" title="Exercise 3 - Hash tables and more bash usage">Exercise 3 - Hash tables and more bash usage</a><ul class="nav">

  672. <li><a href="#Task-1---Hash-tables-in-bash" title="Task 1 - Hash tables in bash">Task 1 - Hash tables in bash</a></li>

  673. <li><a href="#Task-2---Use-sed-in-bash" title="Task 2 - Use sed in bash">Task 2 - Use sed in bash</a></li>

  674. <li><a href="#Task-3---Execute-Python-commands-in-bash" title="Task 3 - Execute Python commands in bash">Task 3 - Execute Python commands in bash</a></li>

  675. </ul>

  676. </li>

  677. <li><a href="#Exercise-4---Debugging-bash-scripts" title="Exercise 4 - Debugging bash scripts">Exercise 4 - Debugging bash scripts</a><ul class="nav">

  678. <li><a href="#Task-1---Command-exit-code" title="Task 1 - Command exit code">Task 1 - Command exit code</a></li>

  679. <li><a href="#Task-2---Using-set--xe" title="Task 2 - Using set -xe">Task 2 - Using set -xe</a></li>

  680. </ul>

  681. </li>

  682. <li><a href="#Questions-to-answer" title="Questions to answer">Questions to answer</a><ul class="nav">

  683. <li><a href="#Bonus" title="Bonus">Bonus</a></li>

  684. </ul>

  685. </li>

  686. </ul>

  687. </li>

  688. </ul>

  689. </div><div class="toc-menu"><a class="expand-toggle" href="#">Expand all</a><a class="back-to-top" href="#">Back to top</a><a class="go-to-bottom" href="#">Go to bottom</a></div>

  690.             </ul>

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  694.         <div class="toc"><ul class="nav">

  695. <li><a href="#Lab-5-Bash-scripting" title="Lab 5: Bash scripting">Lab 5: Bash scripting</a><ul class="nav">

  696. <li><a href="#Exercise-1---Bash-basics" title="Exercise 1 - Bash basics">Exercise 1 - Bash basics</a><ul class="nav">

  697. <li><a href="#Task-1---Bash-scripting-basics" title="Task 1 - Bash scripting basics">Task 1 - Bash scripting basics</a></li>

  698. <li><a href="#Task-2---Bash-loops-and-conditions" title="Task 2 - Bash loops and conditions">Task 2 - Bash loops and conditions</a></li>

  699. <li><a href="#Task-3---If-statements" title="Task 3 - If statements">Task 3 - If statements</a></li>

  700. <li><a href="#Task-4---Bash-functions" title="Task 4 - Bash functions">Task 4 - Bash functions</a></li>

  701. </ul>

  702. </li>

  703. <li><a href="#Exercise-2---Working-with-files-and-directories" title="Exercise 2 - Working with files and directories">Exercise 2 - Working with files and directories</a><ul class="nav">

  704. <li><a href="#Task-1---File-and-directory-test-operators" title="Task 1 - File and directory test operators">Task 1 - File and directory test operators</a></li>

  705. <li><a href="#Task-2---Directory-and-file-manipulation" title="Task 2 - Directory and file manipulation">Task 2 - Directory and file manipulation</a></li>

  706. <li><a href="#Task-3---Jump-directories" title="Task 3 - Jump directories">Task 3 - Jump directories</a></li>

  707. </ul>

  708. </li>

  709. <li><a href="#Exercise-3---Hash-tables-and-more-bash-usage" title="Exercise 3 - Hash tables and more bash usage">Exercise 3 - Hash tables and more bash usage</a><ul class="nav">

  710. <li><a href="#Task-1---Hash-tables-in-bash" title="Task 1 - Hash tables in bash">Task 1 - Hash tables in bash</a></li>

  711. <li><a href="#Task-2---Use-sed-in-bash" title="Task 2 - Use sed in bash">Task 2 - Use sed in bash</a></li>

  712. <li><a href="#Task-3---Execute-Python-commands-in-bash" title="Task 3 - Execute Python commands in bash">Task 3 - Execute Python commands in bash</a></li>

  713. </ul>

  714. </li>

  715. <li><a href="#Exercise-4---Debugging-bash-scripts" title="Exercise 4 - Debugging bash scripts">Exercise 4 - Debugging bash scripts</a><ul class="nav">

  716. <li><a href="#Task-1---Command-exit-code" title="Task 1 - Command exit code">Task 1 - Command exit code</a></li>

  717. <li><a href="#Task-2---Using-set--xe" title="Task 2 - Using set -xe">Task 2 - Using set -xe</a></li>

  718. </ul>

  719. </li>

  720. <li><a href="#Questions-to-answer" title="Questions to answer">Questions to answer</a><ul class="nav">

  721. <li><a href="#Bonus" title="Bonus">Bonus</a></li>

  722. </ul>

  723. </li>

  724. </ul>

  725. </li>

  726. </ul>

  727. </div><div class="toc-menu"><a class="expand-toggle" href="#">Expand all</a><a class="back-to-top" href="#">Back to top</a><a class="go-to-bottom" href="#">Go to bottom</a></div>

  728.     </div>

  729.     <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js" integrity="sha256-hVVnYaiADRTO2PzUGmuLJr8BLUSjGIZsDYGmIJLv2b8=" crossorigin="anonymous"></script>

  730.     <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha256-U5ZEeKfGNOja007MMD3YBI0A3OSZOQbeG6z2f2Y0hu8=" crossorigin="anonymous" defer></script>

  731.     <script src="https://cdnjs.cloudflare.com/ajax/libs/gist-embed/2.6.0/gist-embed.min.js" integrity="sha256-KyF2D6xPIJUW5sUDSs93vWyZm+1RzIpKCexxElmxl8g=" crossorigin="anonymous" defer></script>

  732.     <script>

  733.         var markdown = $(".markdown-body");

  734.         //smooth all hash trigger scrolling

  735.         function smoothHashScroll() {

  736.             var hashElements = $("a[href^='#']").toArray();

  737.             for (var i = 0; i < hashElements.length; i++) {

  738.                 var element = hashElements[i];

  739.                 var $element = $(element);

  740.                 var hash = element.hash;

  741.                 if (hash) {

  742.                     $element.on('click', function (e) {

  743.                         // store hash

  744.                         var hash = this.hash;

  745.                         if ($(hash).length <= 0) return;

  746.                         // prevent default anchor click behavior

  747.                         e.preventDefault();

  748.                         // animate

  749.                         $('body, html').stop(true, true).animate({

  750.                             scrollTop: $(hash).offset().top

  751.                         }, 100, "linear", function () {

  752.                             // when done, add hash to url

  753.                             // (default click behaviour)

  754.                             window.location.hash = hash;

  755.                         });

  756.                     });

  757.                 }

  758.             }

  759.         }

  760. 

  761.         smoothHashScroll();

  762.         var toc = $('.ui-toc');

  763.         var tocAffix = $('.ui-affix-toc');

  764.         var tocDropdown = $('.ui-toc-dropdown');

  765.         //toc

  766.         tocDropdown.click(function (e) {

  767.             e.stopPropagation();

  768.         });

  769. 

  770.         var enoughForAffixToc = true;

  771. 

  772.         function generateScrollspy() {

  773.             $(document.body).scrollspy({

  774.                 target: ''

  775.             });

  776.             $(document.body).scrollspy('refresh');

  777.             if (enoughForAffixToc) {

  778.                 toc.hide();

  779.                 tocAffix.show();

  780.             } else {

  781.                 tocAffix.hide();

  782.                 toc.show();

  783.             }

  784.             $(document.body).scroll();

  785.         }

  786. 

  787.         function windowResize() {

  788.             //toc right

  789.             var paddingRight = parseFloat(markdown.css('padding-right'));

  790.             var right = ($(window).width() - (markdown.offset().left + markdown.outerWidth() - paddingRight));

  791.             toc.css('right', right + 'px');

  792.             //affix toc left

  793.             var newbool;

  794.             var rightMargin = (markdown.parent().outerWidth() - markdown.outerWidth()) / 2;

  795.             //for ipad or wider device

  796.             if (rightMargin >= 133) {

  797.                 newbool = true;

  798.                 var affixLeftMargin = (tocAffix.outerWidth() - tocAffix.width()) / 2;

  799.                 var left = markdown.offset().left + markdown.outerWidth() - affixLeftMargin;

  800.                 tocAffix.css('left', left + 'px');

  801.             } else {

  802.                 newbool = false;

  803.             }

  804.             if (newbool != enoughForAffixToc) {

  805.                 enoughForAffixToc = newbool;

  806.                 generateScrollspy();

  807.             }

  808.         }

  809.         $(window).resize(function () {

  810.             windowResize();

  811.         });

  812.         $(document).ready(function () {

  813.             windowResize();

  814.             generateScrollspy();

  815.         });

  816. 

  817.         //remove hash

  818.         function removeHash() {

  819.             window.location.hash = '';

  820.         }

  821. 

  822.         var backtotop = $('.back-to-top');

  823.         var gotobottom = $('.go-to-bottom');

  824. 

  825.         backtotop.click(function (e) {

  826.             e.preventDefault();

  827.             e.stopPropagation();

  828.             if (scrollToTop)

  829.                 scrollToTop();

  830.             removeHash();

  831.         });

  832.         gotobottom.click(function (e) {

  833.             e.preventDefault();

  834.             e.stopPropagation();

  835.             if (scrollToBottom)

  836.                 scrollToBottom();

  837.             removeHash();

  838.         });

  839. 

  840.         var toggle = $('.expand-toggle');

  841.         var tocExpand = false;

  842. 

  843.         checkExpandToggle();

  844.         toggle.click(function (e) {

  845.             e.preventDefault();

  846.             e.stopPropagation();

  847.             tocExpand = !tocExpand;

  848.             checkExpandToggle();

  849.         })

  850. 

  851.         function checkExpandToggle () {

  852.             var toc = $('.ui-toc-dropdown .toc');

  853.             var toggle = $('.expand-toggle');

  854.             if (!tocExpand) {

  855.                 toc.removeClass('expand');

  856.                 toggle.text('Expand all');

  857.             } else {

  858.                 toc.addClass('expand');

  859.                 toggle.text('Collapse all');

  860.             }

  861.         }

  862. 

  863.         function scrollToTop() {

  864.             $('body, html').stop(true, true).animate({

  865.                 scrollTop: 0

  866.             }, 100, "linear");

  867.         }

  868. 

  869.         function scrollToBottom() {

  870.             $('body, html').stop(true, true).animate({

  871.                 scrollTop: $(document.body)[0].scrollHeight

  872.             }, 100, "linear");

  873.         }

  874.     </script>

  875. </body>

  876. 

  877. </html>