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Advance Linux-Operating System Excercises., Exercises of Computer Science

St. Francis Career College Computer Science

Find Shell Scripts,Writing a Conversion Scripts,Creating a Simple Cryptography Function and Geographic Data Manipulation.

Typology: Exercises

2021/2022

Uploaded on 02/11/2022

oliver97 🇺🇸

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Advanced(Linux:(Exercises( (( 1/6(

Advanced(Linux:(Exercises(

In(these(instructions(the(first(character(“$”(in(the(command(examples(should(not(be(typed,(but(it(

denotes(the(command(prompt.!

Some(command(lines(are(too(long(to(fit(a(line(in(printed(form.(These(are(indicated(by(a(backslash(“\”(at(

the(end(of(line.(It(should(not(be(included(when(typing(in(the(command.(For(example(

$ example command \

continues \

and continues

Should(be(typed(in(as:(

example command continues and continues

0"Download"and"unpack"the"exercise"files"(do"that"first"time"only):"

Go(to(the(workshop(home(page((www.csc.fi(->(click(at(the(workshop(name(link(at(the(right(column,(scroll(

down(and(download(the(tar(archive(from(the(link,(save(as(…)!

Open(a(terminal,(cd(to(the(folder(where(you(downloaded(the(archive,(unzip(and(untar(the(file:!

$ tar xzvf advanced_linux-exercise.tar.gz

The(v((verbose)(flag(in(the(tar(command(shows(the(files(with(the(path(that(are(untarred.(You(see(that(

you'll(get(a(number(of(files(in(a(subdirectory(named(linux-exercises.(Go(to(that(directory(with(the(cd(

command.(

1"Find"shell"scripts"

Metadata:(commands(in(this(exercise:(file,(grep,(wc(

Metadata:(Demonstrate(the(usage(of(pipes(in(simple(tasks(like(finding(the(number(of(certain(files(in(a(

directory.(

1)#How#many#shell#script#files#there#are#in#/usr/bin#directory?#

There(are(quite(a(bunch(of(files(in(/usr/bin,(but(which(of(those(files(are(actually(shell(scripts?(To(find(out(

which(type(a(file(is,(you(will(need(the(file(command,(which(quite(accurately(will(tell(you(what(is(inside(

a(particular(file.(

2"Writing"a"conversion"script"

Metadata:(commands(in(this(exercise:(cp,!convert,!tar,!animate.(

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Download Advance Linux-Operating System Excercises. and more Exercises Computer Science in PDF only on Docsity!

Advanced Linux: Exercises

In these instructions the first character “$” in the command examples should not be typed, but it

denotes the command prompt.

Some command lines are too long to fit a line in printed form. These are indicated by a backslash “\” at

the end of line. It should not be included when typing in the command. For example

$ example command
continues
and continues

Should be typed in as:

example command continues and continues 0 Download and unpack the exercise files (do that first time only):

Go to the workshop home page (www.csc.fi - > click at the workshop name link at the right column, scroll

down and download the tar archive from the link, save as …)

Open a terminal, cd to the folder where you downloaded the archive, unzip and untar the file:

$ tar xzvf advanced_linux-exercise.tar.gz

The v (verbose) flag in the tar command shows the files with the path that are untarred. You see that

you'll get a number of files in a subdirectory named linux-exercises. Go to that directory with the cd

command.

1 Find shell scripts

Metadata: commands in this exercise: file, grep, wc

Metadata: Demonstrate the usage of pipes in simple tasks like finding the number of certain files in a

directory.

1) How many shell script files there are in /usr/bin directory?

There are quite a bunch of files in /usr/bin , but which of those files are actually shell scripts? To find out

which type a file is, you will need the file command, which quite accurately will tell you what is inside

a particular file.

2 Writing a conversion script

Metadata: commands in this exercise: cp, convert, tar, animate.

Metadata: The aim is to present a scripting solution of systematically manipulating a large set of

similarly named files

0) Unpack the jpegs.tar file $ cd FileRename $ tar xvf jpegs.tar 1) Find out what directories and files were created $ ls *.jpg

You find out that the naming is numbered, but the numbering is not in order. Hence, if you produce an

animated gif from this bunch of files using the ImageMagik command convert:

$ convert – delay 30 – loop 2 *.jpg animation_small.gif

you will get strange resulst, as the input jpeg’s are ordered by the first digit, i.e. {0, 10, 11, …, 19, 1, 20,

$ animate animation_small.gif 2) Resize and convert files

This means we want to add a heading 0 to the single-digit numbers to produce the correct order

{00,01,02,03,…,09,10,11,…,50}. Doing that by hand would be tedious, as one would have to make 10

shell commands similar to that on

$ mv 0_singleframe_small.jpg 0 0_singleframe_small.jpg

Additionally, we also can resize the output using the ImageMagik command convert. In a combined way

that would read for single digit numbers (0-9, here using 0):

$ convert – resize 200% 0_singleframe_small.jpg 00_singleframe_large.jpg

as well as for double digit numbers (10-50, here using 10):

$ convert – resize 200% 10_singleframe_small.jpg 10_singleframe_large.jpg

which would force us to give 51 shell commands. But we can use the power of loops within bash! You

need to embed the commands using a variable for the counter within two loops, one from 0 to 9 and

one from 10 to 50. Use the following syntax as a starting point and morph in the commands above:

$ for i in {0..9}; do ls ${i}_singleframe_small.jpg;
echo "converting to 0${i}_singleframe_small.jpg"; done

You can (later on!!) look up the solution in convert.sh.

If there are arguments to the function, then it should read input from the file(s), otherwise it should use

the standard input as a source.

$ rot13 <<< “Make it right once and for all” $ rot13 crypt_input1 crypt_input

Hint: check first if there are any arguments by checking $1. Other variables you need are $@ and $*.

The solutions to each step (2..4) can be found from the files Solution(2..4), respectfully.

4 Geographic data manipulation

Metadata: command in this exercise: wc, head, tail, cat, sort,

gnuplot, pipes

Metadata: The aim is to create use shell text utilities to find certain values

in a dataset.

We will use the dataset from NSDIC that is https://nsidc.org/data/NSIDC-

0119/versions/1 and systematically investigate some properties (max

elevation, ice thickness) using UNIX tools, only. The area (should you be

interested) we investigate is part of the Antarctic ice sheet (see picture right), called Marie Bird Land. If

you want to further use the data in any way, please check the NSDIC web services for their conditions.

Data could be downloaded using the command (just as an example. DON’T DO THAT! – we do not want

to blow up our and NSDIC’s network).

$ wget ftp://sidads.colorado.edu/pub/DATASETS/AGDC/luyendyk_nsidc_0119/*

INSTEAD untar-gzip the provided file:

$ tar xvzf luyendyk_nsidc_0119.tgz

Now we have two ASCII files:

$ ls - l *.txt

rwxrwxrwx 1 root root 170M Mar 9 2004 srfelev.txt
rwxrwxrwx 1 root root 114M Mar 9 2004 icethick.txt

They are large. Check the number of entries (= number of lines) using the wc command. We just want to

work with a smaller sub-set of the data. Hence we reduce the size to the first 1 0 000 lines, only.

$ head – n 10000 srfelev.txt > srfelev_reduced.txt $ head – n 10000 icethick.txt > icethick_reduced.txt

The problem now is, that we do not have a consistent dataset at places (see gnuplot script)

$ gnuplot showdata1.gp

If nothing shows, you might have to install the X11 version of gnuplot, which is done with

$ sudo apt-get install gnuplot-X

(just answer “Y” if asked to download the packages and install).

Hence we would like to reduce the range of both datasets to be confined within - 79.6 and - 79.2 degrees

(southern latitude). Let’s inquire the position within the file for the lower bound:

$ cat - n srfelev_reduced.txt |grep "79.6000"

Output:

2879 - 79.60 0072 - 144.39008 360.9 1137.4 1998 358 10256.30 RTZ8/32\

Wy-Y11a

And the same for ice thickness:

$ cat - n icethick_reduced.txt |grep "79.6000" 1962 - 79.600072 - 144.39008 681.5 1998 358 10256.30 RTZ8/32
Wy-Y11a

So, we have to use the last (10000 – 2879) = 7121 and (10000 – 1962) = 8038 entries.

$ tail - n 7121 srfelev_reduced.txt > srfelev_reduced2.txt $ tail - n 8038 icethick_reduced.txt > icethick_reduced2.txt $ gnuplot showdata2.gp

Now, the same for the upper bound of - 79.2 degrees:

$ cat - n srfelev_reduced2.txt |grep "79.2000" 5892 - 79.200076 - 147.74868 … $ cat - n icethick_reduced2.txt |grep "79.2000" 5739 - 79.200076 - 147.74868 …