Operating systems 1 -- 2009-2010 -- info.uvt.ro/Project 1
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- front;
- laboratories: agenda, 1, 2, 3, 4, evaluation, tools, references, repository;
- projects: 1, 2, repository;
Description
editThe official project description should also be read from profesor Florin Fortiş. Please also consult the references at the end of this page. |
Implement a C application that implements a basic shell that presents a prompter to the user and allows him to enter certain commands (the commands with their syntax and semantics are described in the next section);
The shell should implement the following basic loop:
- write the prompter to the user;
- reads the user command;
- parses and validates the user command;
- in case there is a syntax or semantic error a meaningfull message should be printed to the user;
- executes the user command;
- writes a meaningfull success or failure message for the user;
- the loop should terminate when:
- the user enters exit command; (this is the normal way to close the shell);
- there is an error while reading from stdin (this should be treated as an error, and a meaningfull message should be printed);
- there is an end-of-file encountered in stdin (this should be treated as a warning, but acceptable);
Syntax
editRules:
- each command should be written on its own line:
- commands cannot span multiple lines;
- multiple commands cannot be written on the same line;
- each command is composed of one or more tokens separated by one or more space or tab characters;
- each token is:
- either a sequence of one or more characters except space or tab;
- either a sequence of one or more characters (including space or tab), but enclosed inside double or single quotes; (the quotes are not part of the token, and the quotes character used cannot appear inside the token);
- a line whose first non-space (or tab) character is # should be treated as a comment and ignored;
Examples:
- comment lines:
# this is a comment line
# this is another comment line
##### again a comment line
- simple command without quoted tokens (observe how the whitespace does not matter):
mkdir /tmp/test-folder
rmdir /tmp/test-folder
echo test
exit
- a command with quoted tokens:
# the text enclosed in single quotes is one token (including those double quote characters)
echo ' aaa bb c """"" '
Commands
editList of commands
editgeneric commands | flags | points | |
---|---|---|---|
help | R | ||
version | R | ||
exit | R | ||
file commands | flags | points | man page |
cat | -b, -E, -n, -s | 3 | cat.1 |
tac | -b -s | 3 | tac.1 |
head | -c, -n, -q, -v | 3 | head.1 |
tail | -c, -n, -q, -v | 3 | tail.1 |
sort | -i, -r, -d | 4 | sort.1 |
uniq | -i, -d, -u | 4 | uniq.1 |
nl | -s -d | 2 | nl.1 |
wc | -c, -w, -l, -L | 3 | wc.1 |
expand | -t, -i | 3 | expand.1 |
unexpand | -t, -i, -a | 3 | unexpand.1 |
tee | -a | 3 | tee.1 |
file system commands | flags | points | man page |
cd | 2 | bash.1 (see cd comamnd) | |
pwd | 1 | bash.1 (see pwd comamnd) | |
cp | -i, -R, -t, -v | 5 | cp.1 |
mv | -i, -t, -s | 4 | mv.1 |
rm | -i, -R -v | 4 | rm.1 |
mkdir | -m, -p, -v | 2 | mkdir.1 |
rmdir | -p, -v | 2 | rmdir.1 |
ls | -l, -s, -a, -F | 5 | ls.1 |
dir | 3 | dir.1 | |
chmod | -v, -R | 5 | chmod.1 |
chown | -v, -R | 5 | chown.1 |
chgrp | -v, -R | 5 | chgrp.1 |
dirname | 2 | dirname.1 | |
basename | 2 | basename.1 | |
environment commands | flags | points | man page |
printenv | 2 | printenv.1 | |
env | -u | 3 | env.1 |
miscellaneous commands | flags | points | man page |
yes | 1 | yes.1 | |
date | -d, -f, -s, +<format> | 4 | date.1 |
Generic requirements
edit- each command shall have understand the -h (help flag) -U (user flag) that should provide a short description and usage about the command (-h), or the implementor (-U);
help and version
edit- the help command shall provide a list of available commands and a short description for each one;
- the version command shall print the version, author and other informations about the implementation;
exit
edit- should cause the shell to stop asking for new commands and exit;
- example:
exit
echo
edit- should accept any number of arguments (including none), and display them separated by space;
- example:
echo 'a bb cc' cc d "ee ff"
- output:
a bb cc cc d ee ff
echoenv
edit- should take only one argument that represents the name of an environment variable, and print it to standard output:
- example:
echoenv USER
- output:
ciprian
- example in case of undefined variable:
echoenv NO_SUCH_VARIABLE
- output (to standard error):
[ee] the environment variable `NO_SUCH_VARIABLE` is undefined;
- references:
cd, and pwd
edit- cd should be used to change the current directory to the one pointed by the single argument given;
- pwd should print the current working directory;
- example 1 (both command (prefixed by $, and output (no prefix)):
$ pwd /home/ciprian
- example 2 (both command and output):
$ cd /tmp $ pwd /tmp
mkdir, and rmdir
edit- both take any number of arguments (at least one) and either create or remove the designated folder (rmdir should work only in case of empty directories);
- examples:
$ mkdir /tmp [ee] the folder `/tmp` already exists; $ mkdir /tmp/a /tmp/b /tmp/c $ rmdir /tmp/a /tmp/b $ rmdir /tmp/c $ rmdir /tmp/x [ee] the folder `/tmp/x` does not exist;
touch, link, and unlink
edit- touch creates the designated file in case it does not exist (it accepts more arguments, at least one);
- link takes two arguments (the source and destination) and makes a hard link of the source to destination;
- unlink takes any number of arguments (at least one) and deletes them;
- examples:
$ touch /tmp/a /tmp/b $ link /tmp/b /tmp/c $ unlink /tmp/c
cat, head and tail
edit- cat takes at least one argument and displays the content of each file one after another;
- head takes only one argument and displays the first 10 lines from it;
- tail is like head but displays only the last 10 lines;
- examples:
$ cat /etc/fstab /etc/services ... the content of /etc/fstab ... the content of /etc/services
- head and tail could also accept the -n option, followed by a number and should display that many first or last lines;
- examples:
$ head -n 20 /etc/services ... the first 20 lines from /etc/services
ls
edit- takes exactly one argument, the name of a folder, and should display the files found inside; (by default the folders ., .., and any file / folder starting . should not be displayed;)
- as modifiers (flags) we have:
- -a -- should display even files starting with . (except the . and .. folders);
- -l -- should display after each file the type, owner (uid), group (gid) and size;
- the contents should be sorted alphabeticaly;
- examples:
$ ls / dev etc tmp var ... $ ls -a /home/ciprian .bashrc .bash_login ... desktop ... $ ls -l /boot grub folder 0 0 4096 vmlinuz file 0 0 13341253
cp, and mv
edit- cp takes exactly two arguments: the source and destination, and it should copy the content of the source file as the content of the destination file;
- if the destination file already exists it should be treated as an error;
- if -f flag is present the copy is forced (even if the destination already exists);
- mv is the same as cp, but instead of copying it moves the file;
- mv should not be implemented by using the rename POSIX function (or by link and unlink); instead a new file must be created, filled with the contents of the old one; and then the old file should be deleted;
Notes
editMandatory observations:
- all messages that are meant for the user to see (informations, warnings, errors, etc.) should be printed to stderr;
- all text that is part of the command actual output (like in the case of ls) should be printed to stdout;
- stdin should be only used to read user commands;
Optional observations:
- in case of messages for the users it would be nice to prefix the text with an indicator of the nature / gravity of the message; for example for informative messages (like success) you could prepend one of the following prefixes: INFO:, or [ii], etc. (a space would be nice between the prefix and the actual output);
References
edit- from me:
- Operating systems 1 -- 2009-2010 -- info.uvt.ro/Laboratory 2 -- the POSIX functions used there for file system management;
- Operating systems 1 -- 2009-2010 -- info.uvt.ro/Laboratory 3 -- the additional readline and getopt helper functions;
- from Florin Fortiş:
- from Silviu Panica:
- SO1 ENG:
- Laboratory 4 -- building process;
- Laboratory 5 -- shell skeleton and readline;
- Laboratory 6 -- getopt, environment variables, directories;
- SO1 ENG:
[parse the farse 1]Submission
editPlease consult the repository page.
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