Description
Solve the following questions. A portion of your m
ark for the assignment will be for correctly follo
wing the directions. Each question specifies the s
ystem that is to be used to complete that question
..
This question can be completed on either tuxworld
or on an ismac computer. The solution should be th
e same.
Suppose you have a file named myfile in your curre
nt working directory. List three different non-err
oneous commands you could use to view the file myf
ile using the less command. The three commands mus
t exemplify three different types or forms of comm
ands, and the output from less must be made to you
r virtual terminal (and not to a file or piped to
another process). Remember that the context for th
is question is LINUX on tuxworld.
For the purposes of this question, the “form or typ
e of command” is determined by:
whether one (child) process is created to perform
the command (this is one possibility) or multiple
processes (children) are created to perform the co
mmand (the other possibility);
the presence (one possibility) or lack (the other p
ossibility) of pipes in the command;
whether or not less(1) gets its input from a file
specified as an argument (one possibility) or from
its stdin (the other possibility).
If a set of choices for the above possibilities ar
e different for one command than they are for anot
her command, then those two commands are “of a dif
ferent type”. However, the options given to expand
(1) are not used to determine the “type of command
” in this question.
Also for the purposes of this question,
when less(1) executes according to your command, i
ts standard output must be (bound to) your virtual
terminal (in which you are executing the command);
your commands cannot use command substitution subs
hells, or (the built-in command) exec, if you happ
en to already know what any of those are);
there can be only one instance of less in the pipel
ine;
whether or not the commands execute in the foregro
und or background is irrelevant to this question;
the settings of environment variables used by less(
1) are irrelevant to this question.
Remember to consult the man page for less(1) to fi
nd out more information about the command.
Submit a file q1_solution.txt containing your three
commands.
Note that on tuxworld, there are two programs for
perusing a file: a simpler one named more, and a m
ore feature-full one named less. This is different
than the situation on BSD UNIX systems as exhibit
ed, for example, by Mac OS X where more(1) and les
s(1) are exactly the same program.
The context for this question is Mac OS X. Therefo
re, complete this question on an ismac computer.
There is no option to the ls command telling it to
only output the names of directories. For example
, suppose that, given the current working director
y of a user, ls behaves as follows:
bash-3.2$ ls -l
total 1
-rw-r–r– 1 kusalik cmpt214 2619 13 Oct 2012
LatePenalty.html
drwxr-xr-x 10 kusalik cmpt214 340 7 Nov 2012
assignment_1
drwxr-xr-x 12 kusalik cmpt214 408 4 Nov 2012
assignment_2
drwxr-xr-x 31 kusalik cmpt214 1054 20 Nov 2012
assignment_3
drwxr-xr-x 20 kusalik cmpt214 680 4 Dec 2012
assignment_4
-rw-r–r– 1 kusalik cmpt214 830 14 Oct 2012
external_documentation.txt
-rw-r–r–@ 1 kusalik cmpt214 9368 23 Jan 2014
extra questions.txt
drwxr-xr-x 2 kusalik cmpt214 68 24 Sep 14:01
test this
-rw-r–r–@ 1 kusalik cmpt214 2525 1 Dec 2012
testing_documentation.html
bash-3.2$ ls
LatePenalty.html external_documentation.txt
assignment_1 extra questions.txt
assignment_2 test this
assignment_3 testing_documentation.html
assignment_4
Write a UNIX command pipeline that will result in
just the directories being listed in the output th
at originates with ls. For example, in the situati
on described above, the pipeline will produce
assignment_1 assignment_2 assignment_3 assignmen
t_4 test this
As another example, suppose the current working di
rectory is the root directory of a particular Mac
OS X system and ls produces the following output:
bash-3.2$ cd /
bash-3.2$ ls
Applications etc
Archive hide
Library home
Network installer.failurerequests
Previous Systems net
System opt
Users private
Volumes sbin
bin tmp
cores usr
dev var
bash-3.2$ ls -l
total 1
drwxrwxr-x+ 123 root admin 4182 25 Jul 06:11 Appl
ications
drwxrwxrwx 6 root wheel 204 17 Feb 2008 Arch
ive
drwxr-xr-x+ 78 root wheel 2652 14 Feb 2016 Libr
ary
drwxr-xr-x@ 2 root wheel 68 9 Sep 2014 Netw
ork
drwxrwxr-x 10 root wheel 340 12 Mar 2014 Prev
ious Systems
drwxr-xr-x+ 4 root wheel 136 30 Jul 2015 Syst
em
drwxr-xr-x 11 root admin 374 14 Feb 2016 User
s
drwxrwxrwt@ 4 root admin 136 24 Sep 10:05 Volu
mes
drwxr-xr-x@ 39 root wheel 1326 22 Aug 2015 bin
drwxrwxr-t@ 2 root admin 68 9 Sep 2014 core
s
dr-xr-xr-x 3 root wheel 4360 2 Sep 06:50 dev
lrwxr-xr-x@ 1 root wheel 11 30 Jul 2015 etc
-> private/etc
drwxr-xr-x 2 root wheel 68 30 Jul 2015 hide
dr-xr-xr-x 2 root wheel 1 24 Sep 10:10 home
-rw-r–r–@ 1 root wheel 313 1 Oct 2014 inst
aller.failurerequests
dr-xr-xr-x 2 root wheel 1 24 Sep 10:10 net
drwxr-xr-x@ 4 root wheel 136 12 Mar 2014 opt
drwxr-xr-x@ 6 root wheel 204 30 Jul 2015 priv
ate
drwxr-xr-x@ 59 root wheel 2006 22 Aug 2015 sbin
lrwxr-xr-x@ 1 root wheel 11 30 Jul 2015 tmp
-> private/tmp
drwxr-xr-x@ 15 root wheel 510 5 Nov 2015 usr
lrwxr-xr-x@ 1 root wheel 11 30 Jul 2015 var
-> private/var
In this situation, your pipeline would produce
Applications System dev
private
Archive Users hide
sbin
Library Volumes home
usr
Network bin net
Previous Systems cores opt
However, if the current working directory contains
no subdirectories, your pipeline will produce not
hing or else a blank line as output.
The number of columns will be determined automatic
ally by one of the programs in your program.
Place your pipeline in a file q2_answer.txt. Test
your pipeline and place an annotated test log in a
file q2_log.txt. Submit these two files.
Hints:
Use the UNIX command “rs” (with no options or argu
ments) in your pipeline. Make sure to check the ma
n page for rs to find out what it does. rs(1) is n
ot available on LINUX. If you use the -t option to
rs, your output should still be placed in columns
but your pipeline may not correctly handle file n
ames with spaces in them.
Make sure to test your pipeline in directories con
taining subdirectories with various ownership, and
in particular, variation in the length of user or
group names.
In pursuing this problem, we suggest that you adhe
re to the process of incremental software developm
ent, successively building up the command, verifyi
ng that each successive addition works with a vari
ety of input, and gradually building towards the f
inal solution.
The tee command is sometimes useful for testing an
d verification of pipelines, by allowing you to re
cord the output of intermediate points in the pipe
line, while still providing that output on to late
r commands.
The fragment of Procedural C++ code in file q3_ini
tial.cc contains several violations of the program
ming style guidelines given in class. Identify as
many of these violations as you can, and then rewr
ite the code fragment using better programming sty
le. Consider for improvement not only the executab
le statements, but the comments as well. Do not ch
ange any of the program logic; i.e. the overall co
ntrol flow and design should remain the same. Plac
e your corrected or improved program in a file q3_
final.cc.
In a file name d q3_solution.txt described all the
style violations you identified. Make each descri
ption concise, but be clear about what lines or st
atements are being referenced or discussed. If you
find multiple instances of the same type of probl
em, report it in general terms just once.
Submit your q3_solution.txt and q3_final.cc.
Hint: how might “-x option to more(1) or less(1) be
useful in this question?
This question can be completed on either tuxworld
or on an ismac computer. The solution should be th
e same.
In class, we used a construction such as
egrep ‘\<[0-9]{1,2}\>‘ <<< 0
egrep -v '\<[0-9]{1,2}\>‘ <<< 199
to test regular expressions given to grep(1) (and
egrep). Suppose that you are using an old version
of bash(1) wherein the construct <<< does not exis
t. Another way to perform the same test, but with
a different type of command would be
egrep '\<[0-9]{1,2}\>‘ << EOF
0
EOF
and
egrep -v '\<[0-9]{1,2}\>‘ << EOF
199
EOF
The above makes use of a construct called a "here
document". (See pages 450 to 451 of the Sobell tex
t for an explanation of "here documents".) Give ye
t another type of shell command that will perform
the same test as
egrep '\<[0-9]{1,2}\>‘ <<< 0
but this time not using <<< , << , <, or a file. T
hat is, egrep(1) will test an input string provide
d on its standard input against a regular expressi
on given as its argument. The input, in this case
"0", is provided as part of the command you need t
o create/compose. The output of the command will b
e "0" on the standard output if the string "0" is
matched by the regular expression '\<[0-9]{1,2}\>‘
. If it does not match, no output appears on the s
tandard output.
Then give a shell command of the identical type tha
t will perform the same test as
egrep -v ‘\<[0-9]{1,2}\>‘ <<< 199
In neither case can you can use a temporary file. N
or can you use the << or < constructs.
Hint: continue to use egrep (or grep) but consider
using a pipe.
Hint: invoking egrep (or grep) with different opti
ons than shown above is not a solution to this que
stion. Further, the correct solution does not invo
lve any options to egrep (or grep) than those show
n above.
Submit your two commands in a file named q4_soluti
on.txt and a log of testing your commands in a fil
e named q4_log.txt.
General Notes:
Electronic submissions are to be made using the moo
dle pages for the class.
All of the files you upload as part of your assign
ment solution are to be in plain ASCII text format
.
Luxuriantly hand-crafted from only the finest HTML
tags by ...
kusalik @ cs (.usask.ca)
