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Assignment 1  Process Creation and Inter-Process Communication

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CSI 3131 Assignment 1
Process Creation and Inter-Process Communication
Goal
Practice process creation and communication in Linux using fork() and exec() system
calls.
Description
Please read the complete assignment document carefully before starting.
Write a C program dp (standing for double pipe) with the following command syntax:
dp program1 <arglist1 : program2 <arglist2 : program3 <arglist3
where
• program1, program2 and program3 are executable program files
• arglist1, arglist2 and arglist3 are the command line arguments of the
corresponding programs
o you may assume that the arguments do not contain characters “ and :
• programk <arglistk means execution of programk with the command line
arguments from arglistk, for a given k from {1,2,3}
Your program dp shall launch programk <arglistk for k=1..3. (i.e. launch three
programs, each with its command line arguments)
In addition, the following requirements must be fulfilled:
1. program2 <arglist2 is executed with the standard input coming from the standard
output of program1 <arglist1
2. program3 <arglist3 is executed with the standard input coming from the standard
output of program1 <arglist1
3. program2 and program3 do not divide the output of program1 among themselves,
they both get the full output of program1
Examples:
4. dp ls -l : grep txt : grep doc
o launches ls –l, that will list the current directory
o the output is sent to grep txt, which will output only the lines containing
substring ‘txt’
o the output is sent also to grep doc, which will output only the lines
containing substring ‘doc’
o as a result, information about all files of the current directory containing
txt or doc in their filename will be outputted (if a file contains both txt and
doc, it will be outputted twice)
o in particular, if your folder has the following files:
o then your program should get the following outputs:
5. dp cat /proc/cpuinfo : grep cpu : grep bug
o the result should be similar to:
Background information:
1. You will need the following C library functions:
a. fork() – should be familiar from lectures
b. pipe() – should be familiar from lectures (note, remember that multiple
process can be attached to each end of the pipes, which means that a pipe
is maintained until no processes are connected at either end of the pipe)
c. execvp(const char * program, const char *args[])
• replaces the current process with the program from the file specified in
the first argument
• the second argument is a NULL terminated array of strings
representing the command line arguments
• by convention, args[0] is the file name of the file to be executed
d. dup2(int newfd, int oldfd) – duplicates the oldfd by the newfd and closes
the oldfd. See http://mkssoftware.com/docs/man3/dup2.3.asp for more
information..
e. read(int fd, char *buff, int bufSize) – read from the file (or pipe) identified
by the file descriptor fd bufSize characters into the buffer buff. Returns the
number of bytes read, or -1 if error or 0 if the end of file has been reached
(or the write end of the pipe has been closed and all data read).
f. write(int fd, char *buff, int buffSize) – write into the file/pipe buffSize
characters from the buffer buff
g. close(int fd) – close an open file descriptor
2. Each process has by default three open file descriptors:
a. Standard input (file descriptor 0, i.e. read(0,buf, 4) reads 4 characters from
the standard input to the buffer buf)
b. Standard output (file descriptor 1)
c. Standard error (file descriptor 2)
d. When a command is run from the shell, the standard input, standard ouput
and standard error are connected to the shell tty (terminal). So reading the
standard input reads from the keyboard and writing to the standard ouput
or standard error writes to the display.
e. From the shell it is possible to connect the standard output from one
process to the standard output to another process using the pipe “|”. For
example, the command “who | wc” connects the standard output from the
who process to the standard input of the wc process such that any data
written to the standard output by the who process is written (via a pipe) to
the standard input of the wc process.
To complete the assignment:
1. Start with the provided file dp.c. It includes all the header files you need, as well
as the code for parsing the command line arguments.
2. You need to enter the name and student ID in the description area of the file dp.c
3. Implement the procedure doublePipe().
4. Submit the resulting file dp.c (DO NOT COMPRESS IT)

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