Skip to content

Commit 8d6da81

Browse files
janpgitjanpgit
committed
A labs assignment defined now.
1 parent 3282c15 commit 8d6da81

File tree

2 files changed

+318
-0
lines changed

2 files changed

+318
-0
lines changed

‎docs/class-assignments/labs-assignment-2018.txt‎

Lines changed: 313 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,313 @@
1+
Labs Assignment for 2018 - Simple Shell
2+
=======================================
3+
Write a simple Unix/Linux shell.
4+
5+
When you are done, we prefer to get a link to you github project but you
6+
can send it to us via email (a single tar file) as well. Your project
7+
must provide a Makefile so that running the "make" command does build
8+
the shell in the binary called 'mysh' (this saves us the work when running
9+
automated tests).
10+
11+
The first phase must be finished and handed to us before the end of the
12+
Winter semester, ie. Jan 13, 2019. All examples shown below must work
13+
as expected.
14+
15+
The second phase must be finished and handed over to us before the end
16+
of the Summer semester, ie. by June 30, 2019.
17+
18+
The deadlines are hard requirements, please stick to the schedule.
19+
20+
Obviously, you can send us the whole thing in one step before the first
21+
deadline, no need to separate the project in two parts.
22+
23+
If in doubt, please ask a question.
24+
25+
C Style
26+
-------
27+
Please choose a good C style, for example http://mff.devnull.cz/cstyle/,
28+
or pick another existing cstyle (e.g. https://man.openbsd.org/style).
29+
Please do not invent your own C style.
30+
31+
Implementation notes
32+
--------------------
33+
We are interested in you dealing with the Unix/Linux stuff you learn in
34+
the class, so please do not spend time writing a linked list
35+
implementation or a command line parser (the latter is much harder that
36+
one might think).
37+
38+
For getting the input line, we recommend the readline library, see "man
39+
readline". You should find it on any Linux, *BSDm, MacOS, or Solaris
40+
machine. By using readline, you get line editing, history, completion,
41+
etc. for free. Another alternative is libtecla.
42+
43+
For tokenizing and parsing the command line, we suggest you to use
44+
GNU flex(1) and bison(1). They are easy to use and you should also find
45+
it virtually everywhere, already installed. We recommend O'Reilly's
46+
book "flex & bison", the first 30 pages should be all you need for this
47+
project. I believe you can find the book online.
48+
49+
You will probably need a linked list implementation. We suggest you use
50+
macros from <queue.h>, those are proven macros. See "man queue" for
51+
more information. STAIL_* macros should be all you need.
52+
53+
FYI, our implementation of the complete 1st phase is 550 lines long,
54+
including flex and bison source files, and using the usual C style from
55+
http://mff.devnull.cz/cstyle/.
56+
57+
It goes without saying it is an individual, not a team project. Do not
58+
use code written by other fellow students. The idea is you learn by
59+
coding your own project.
60+
61+
Test scenario
62+
-------------
63+
Use any Unix/Linux/MacOS system you want but make sure your code builds
64+
and works on a Linux machine in the MFF UK lab, e.g.
65+
u-pl1.us.oracle.com.
66+
67+
Use Valgrind to make sure you do not mismanage memory. Valgrind is
68+
installed on machines in the MFF UK Unix lab.
69+
70+
Phase 1
71+
-------
72+
Note - the "mysh$" prompt in examples below represents the behavior of
73+
the shell you implement. The "Bash$" prompt represents the system shell
74+
you start your shell from.
75+
76+
- Honor and use the existing PATH you get from your parent shell, i.e.
77+
so that one can use "ls" and the command will execute.
78+
79+
- ^C (= SIGINT) in the prompt kills the current unfinished line and
80+
offers a new prompt (same way as bash does it). E.g:
81+
82+
mysh$ ls xxx^C
83+
mysh$
84+
85+
- An empty command just prints a new prompt (as bash does it). E.g.
86+
87+
mysh$ <SPACE><SPACE><SPACE><ENTER>
88+
mysh$
89+
90+
- Implement simple foreground command execution. Commands may be
91+
separated with a semicolon. Any number of commands separated by a
92+
semicolon must be supported (i.e. until you reach some other system
93+
limits):
94+
95+
- i.e. "cmd [; cmd2 [; cmd3 ...]]]
96+
- for example:
97+
98+
mysh$ date
99+
Mon Oct 8 04:51:27 PDT 2018
100+
mysh$
101+
102+
mysh$ /usr/bin/echo X
103+
X
104+
mysh$
105+
106+
mysh$ echo X; date; echo Z
107+
X
108+
Monday, October 8, 2018 at 11:36:04 AM CEST
109+
Z
110+
mysh$
111+
112+
Whitespace should not matter, i.e.:
113+
114+
mysh$ echo X;date;echo Z
115+
X
116+
Monday, October 8, 2018 at 11:36:04 AM CEST
117+
Z
118+
mysh$
119+
120+
- A semicolon after the last command is legal (as is in bash). E.g:
121+
122+
mysh$ echo x;
123+
x
124+
125+
However, the following is not legal:
126+
127+
mysh$ date;;
128+
error:1: syntax error near unexpected token ';'
129+
mysh$
130+
131+
- Implement an internal "exit" to exit the shell. E.g.:
132+
133+
Bash$ ./mysh
134+
mysh$ exit
135+
Bash$ echo $?
136+
0
137+
Bash$
138+
139+
- ^D (i.e. Ctrl-D) exits the interactive shell as well (same as the
140+
"exit" internal command). Again, see bash for an example.
141+
142+
- Implement an internal "cd" command. It works in three modes:
143+
144+
- "cd" goes to $HOME
145+
- "cd -" goes to previous directory
146+
- "cd <dir>" goes to "<dir>"
147+
148+
149+
The internal cd must set the PWD and OLDPWD environment variables
150+
(again see bash).
151+
152+
E.g.:
153+
154+
mysh$ pwd
155+
/data/maish
156+
mysh$ cd
157+
mysh$ pwd
158+
/home/jpechane
159+
mysh$ cd -
160+
mysh$ pwd
161+
/data/maish
162+
mysh$ cd /tmp
163+
mysh$ pwd
164+
/tmp
165+
mysh$ cd -
166+
mysh$ pwd
167+
/data/maish
168+
169+
- The "-c" option is supported as in any other usual shell.
170+
171+
E.g.:
172+
173+
Bash$ mysh -c "echo XXX; date"
174+
XXX
175+
Monday, October 8, 2018 at 1:36:56 PM CEST
176+
Bash$
177+
178+
- The '#" comment is supported. E.g.:
179+
180+
mysh$ echo X # comment
181+
X
182+
mysh$ # another comment
183+
mysh$
184+
185+
Or:
186+
187+
./mysh -c 'date; echo X # comment'
188+
Wednesday, October 10, 2018 at 10:10:09 AM CEST
189+
X
190+
191+
Comments must also work in the non-interactive mode, see below.
192+
193+
- The non-interactive mode is supported.
194+
195+
- i.e. 'mysh test.sh' must work and the commands from the file
196+
are executed sequentially.
197+
198+
- the shell errors out on first syntax error as a usual shell
199+
does. E.g:
200+
201+
Bash$ cat test.sh
202+
echo X
203+
date
204+
;;
205+
echo Y
206+
207+
Bash$ ./mysh test.sh
208+
X
209+
Monday, October 8, 2018 at 11:38:16 AM CEST
210+
error:3: syntax error near unexpected token ';'
211+
Bash$
212+
213+
- shell must treat syntax errors gracefully. Print the line
214+
number where the problem occured. See the error message
215+
above.
216+
217+
- In all modes, the return value of your shell is the return value of
218+
the last command (or pipeline) executed or some specific error on a
219+
syntax error (e.g. bash returns 2, ksh returns 3). E.g. if we use
220+
return value of 254 for a syntax error, it will look like this:
221+
222+
Bash$ ./mysh -c "grep XXX123 /etc/passwd"
223+
Bash$ echo $?
224+
1
225+
226+
Bash$ ./mysh -c ';;'
227+
error:1: syntax error near unexpected token ';'
228+
Bash$ echo $?
229+
254
230+
231+
mysh$ grep XXX123 /etc/passwd
232+
mysh$ exit
233+
Bash$ echo $?
234+
1
235+
236+
mysh$ grep XXX123 /etc/passwd
237+
mysh$ ^D
238+
Bash$ echo $?
239+
1
240+
241+
mysh$ ls; ;
242+
error:1: syntax error near unexpected token ';'
243+
mysh$ exit
244+
Bash$ echo $?
245+
254
246+
247+
- return value of unknown command is 127 (as in bash). E.g:
248+
249+
Bash$ ./mysh -c 'xxx123'
250+
mysh: xxx123: No such file or directory
251+
Bash$ echo $?
252+
127
253+
254+
- error and warning messages from the shell itself go to standard error
255+
output. E.g. the message "mysh: xxx123: No such file or directory"
256+
from above goes to stderr.
257+
258+
- the interactive shell must handle SIGINT well (= killing the
259+
foreground process via ^C). I.e.:
260+
261+
mysh$ sleep 100
262+
^CKilled by signal 2.
263+
mysh$
264+
265+
However, also see the paragraph about killing the unfinished command
266+
line with ^C. Both must work as explained.
267+
268+
The "Killed by..." message also goes to stderr.
269+
270+
- it would be nice if you put the current working directory in the
271+
prompt, like this:
272+
273+
mysh:/data/mysh$ cd /
274+
mysh:/$ cd /tmp
275+
mysh:/tmp$
276+
277+
Phase 2
278+
-------
279+
- pipes
280+
- redirections (>, <, >>)
281+
- background execution via &
282+
283+
Specific examples will be provided till the end of November but it must
284+
work in the usual fashion. For example, this works in any normal
285+
Unix/LInux shell, i.e. the redirection does not have to be at the end:
286+
287+
mysh$ > output date
288+
mysh$ cat output
289+
Wednesday, October 10, 2018 at 10:12:53 AM CEST
290+
291+
And pipelines may be separated by a semicolon, i.e. it's an extension of
292+
the 1st phase:
293+
294+
mysh$ cat /etc/passwd | wc -l; echo X | grep X
295+
26
296+
X
297+
298+
Anything not listed is not required
299+
-----------------------------------
300+
I.e. we do NOT require any of these below:
301+
302+
- variable support (i.e. "echo $HOME" nor "XXX=value ./a.out")
303+
- "export" internal command
304+
- job control
305+
- support for $? etc.
306+
- strings, i.e. the following is not required:
307+
308+
$ echo "xxx yy"
309+
xxx yy
310+
- `` and $( ... )
311+
312+
vim:tw=72
313+
vim:ft=conf

‎docs/index.html‎

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -105,6 +105,11 @@ <h2><a name="practices">Practices and class assignments</a></h2>
105105
<p>Assignments from the labs: <a
106106
href="https://github.com/devnull-cz/unix-linux-prog-in-c-labs">unix-linux-prog-in-c-labs@github</a>
107107

108+
<p>The labs assignment you need to implement to get credits for the labs (which
109+
is a hard dependency for entering the credits that you get for passing the exam
110+
into the school information system) is a <a
111+
href="./class-assignments/labs-assignment-2018.txt">simple Unix/Linux shell.</a>
112+
108113
<a name="consultations"><h2>Consulations</h2></a>
109114

110115
<p>Via email or after a lecture or practice.

0 commit comments

Comments
 (0)