You are to write a C program that will essentially read a text file for a list of
commands and will execute those commands in a pipeline:
cmd1 | cmd2 |cmd3………….| cmdn
First pass:
congaline1.c This version does not need to handle the situation where the
cmd’s have arguments. It reads the textfile containing the commands from
stdin. To (minimally) test your program we suggest you write 3 small
programs:
addone.c that reads (text) integers from stdin and writes those integers
(incremented by one) to stdout.
addone_in.c that opens an inputfile (“inputfile” – “hard wired” into the
program) and reads (text) integers from the file and writes those integers
(incremented by one) to stdout.
addone_out.c that opens an outputfile (“outputfile” – “hard wired into the
program) and reads text integers from stdin and writes those integers
(incremented by one) to the opened file.
If you have written congaline1.c properly then if “inputfile” contains the
number 1 and the textfile of commands contains:
./addone_in
./addone
./addone
./addone
./addone_out
then after running conglaline1 outputfilename
or
./addone outputfilename
or
./addone –i inputfilename
./addone
./addone
./addone
./addone –o outputfilename
Extra challenge (again not marked)
– dream up some more interesting examples that actually do something
useful with standard unix commands piped together.
Submission – instructions will be posted shortly.
HINT Pseudo-code to create a set of cmds piped:
for cmd in cmds
if there is a next cmd
pipe(new_fds)
fork
if child
if there is a previous cmd
dup2(old_fds[0], 0)
close(old_fds[0])
close(old_fds[1])
if there is a next cmd
close(new_fds[0])
dup2(new_fds[1], 1)
close(new_fds[1])
exec cmd || die
else // is parent
if there is a previous cmd
close(old_fds[0])
close(old_fds[1])
if there is a next cmd
old_fds = new_fds
if there are multiple cmds
close(old_fds[0])
close(old_fds[1])
see: http://stackoverflow.com/questions/916900/having-trouble-with-fork-pi
pe-dup2-andexec-in-c/ (Links to an external site.)Links to an external site.
Detailed Submisison Instructions
The handin key for this exercise is: prac2. The following SVN commands will
enable you to make a repository for this assignment. Please note the
following:
• Perform. these steps in the order written once only!
• Replace aaaaaa, where it appears in the commands, with YOUR student id.
• Some commands are long — they must be typed on one line.
Use the Unix “cd” command to change to the place where you want your
exercise directory to be stored, then type these commands:
svn mkdir --parents -m "spc prac2 start"
https://version-control.adelaide.edu.au/svn/a1aaaaaa/2018/s1/spc/prac2
(creates this directory in your svn tree)
svn
co https://version-control.adelaide.edu.au/svn/a1aaaaaa/2018/s1/spc/prac2
.
(checks out a working copy in your directory) You can now begin work.
You can add a file to the repository by typing the commands:
svn add NAME-OF-FILE
svn commit -m "REASON-FOR-THE-COMMIT"
where “reason-for-the-commit” should be some brief text that explains why
you changed the code since the last commit. Note that you only need to add
a file once — after that, SVN will “know” it is in the repository. You are now
ready to commence working on the exercise.
The files you handin must include:
1. Your C source files as specified above.
2. A Makefile that will compile your C sources as specified above.
You do not have to include any of the add_one.c files or their variants... that
you used for testing we will supply those.