Lab 3: Process Management System Calls

CSC 33200 (L) - Operating Systems 
Lab 3: Process Management System Calls

This handout describes the exec family of functions, for executing a comand. You can use
these functionsto make a child process execute a new program after it has been forked. The
functions in this family differ in how you specify the arguments, but otherwise they all do
the same thing. They are declared in theheader file 'unistd.h'.
execv (char *filename, char *const argv[])
The execvfunction executes the file named by filename as a new process image.
The argv argument is an array of null-terminated strings that is used to provide a value
for the argv argument to the main function of the program to be executed. The last element
of this array must be a null pointer.
execvp (char *filename, char *const argv[])
The execvp function is similar to execv, except that it searches the directories listed in the
PATH environment variable to find the full file name of a file from filename if filename
does not contain a slash.
This function is useful for executing system utility programs, because it looks for them in
the places that the user has chosen. Shells use execvpto run the commands that
users type.
execl (char *filename, const char *arg0, ...)
This is similar to execv, but the argv strings are specified individually instead of as an
array. A null pointer must be passed as the last such argument.
execlp (char *filename, const char *arg0, ...)
This function is like execl, except that it performs the same file name searching as
the execvp function.
Example 1: Using execv(...) command
Note: This version will not search the path, so the full name of the executable file must be
given. Parameters to main() are passed in a single array of character pointers.
#include <unistd.h>
#include <stdio.h>
int main(int argc, char* argv[]){
 execv("/bin/echo", &argv[0]);
 printf("EXECV Failed\n");
 return 0;
}
./example1.out “Hello World”
Example 2: Using execvp(...) command
Note: This version searches the path, so the full name of the executable need not be given.
Parameters to main() are passed in a single array of character pointers. This is the form
used inside a shell!
#include <unistd.h>
#include <stdio.h>
int main(int argc, char* argv[]){
 execvp("echo", &argv[0]);
 printf("EXECVP Failed\n");
 return 0;
}
./example2.out “Hello World”
TASK 3. Marks: 20
Part 1 Write a program where a child is created to execute command that tells you the date
and time inUnix.
Use execl(...).
Note, you need to specify the full path of the file name that gives you date and time
information.Announce the successful forking of child process by displaying its PID.
Part 2 Write a program where a child is created to execute a command that shows all files
(including hid-den files) in a directory with information such as permissions, owner,
size, and when last modified.
Use execvp(...).
For the command to list directory contents with various options, refer the handout
on Unix filesystem sent to you in the first class.
Announce the successful forking of child process by displaying its PID.
Part 3
[Step 1] Prcs_P1.c: Create two files namely, destination1.txt and destination2.txt with
read, write,and execute permissions.
[Step 2] Prcs_P2.c: Copy the contents of source.txt1 into destination1.txtand
destination2.txtasper the following procedure.
1. Read the next 100 characters from source.txt, and among characters read, replace
each char-acter ’1’ with character ’L’ and all characters are then written in
destination1.txt
2. Then the next 50 characters are read from source.txt, and among characters read,
replace each character ’3’ with character ’E’ and all characters are then written in
destination2.txt.
3. The previous steps are repeated until the end of file source.txt. The last read may
not have100 or 50 characters.
Once you’re done with successful creation of executables for the above two steps do the
following.
Write a C program and call it Parent_Prcs.c. Execute the files as per the following
procedure using
execv system call. Use sleep system calls to introduce delays.
[Step 3] Using fork create a child process, say Child 1 that executes Prcs_P1. This
will create two destinationfiles according to Step 1.
[Step 4] After Child 1 finishes its execution, use fork to create another child process,
say Child 2 and execute
Prcs_P2that accomplishes the procedure described in Step 2.
Submission Instructions
• You should use only file management system calls for file manipulation
• Use the given source.txt
• All the programs MUST be clearly indented and internally documented
• Make sure your programs compile and run without any errors
• Save all your programs with meaningful names and zip into a single
folder as: task3_[your last name here].zip (e.g., task3_Xyz.zip)
• Email your code with the subject line, "Task3-CSC33200(L)–Class#
12345-lastname" (e.g., Task3 - CSC33200(L)-Class #63858-Xyz)
• Email: sdebnath@ccny.cuny.edu
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