![Write a C program called pross.c to implement the UNIX/Linux equivalent shell commands:
ls -al / | grep -i s | tr a-z A-Z
The symbol “|― is the Linux pipe command.
The signature of the main program:
int main (int argc, char *argv[]) {
}
Where:
•  argc is the number of arguments that are passed to the program plus 1
•  argv[0] is the name of the program
A template of the main program and its functions are provided to you along with this document
on Blackboard. Use the following system calls to implement the shell commands:
o  dup2()
o  one of the exec()
o  fork()
o  pipe()
o  close()
pross.c
Solution
In the c programming the shell commands can't be executed directly, but there are several other
options to get implemented.
1. Do not use the shell , but bypass the shell and run the commands driectly with specified
program.Many of the basic utilities can be accessed easily enough and system calls are available
for system programming tasks.You need to use pipe() ,fork () and exec().
2. Use system() to run the command if input and output are not important.
3.use poopen () if control on either input or output is needed.
4. run the shell as a coprocess.
If we select to bypass the shell, it can be bit easier to have buffered.](https://image.slidesharecdn.com/writeacprogramcalledpross-ctoimplementtheunix-linuxequivalen-230209234105-cd900f68/85/Write-a-C-program-called-pross-c-to-implement-the-UNIX-Linux-equivalen-docx-1-320.jpg)
Write a C program called pross-c to implement the UNIX-Linux equivalen.docx
- 1. Write a C program called pross.c to implement the UNIX/Linux equivalent shell commands: ls -al / | grep -i s | tr a-z A-Z The symbol “|― is the Linux pipe command. The signature of the main program: int main (int argc, char *argv[]) { } Where: •  argc is the number of arguments that are passed to the program plus 1 •  argv[0] is the name of the program A template of the main program and its functions are provided to you along with this document on Blackboard. Use the following system calls to implement the shell commands: o  dup2() o  one of the exec() o  fork() o  pipe() o  close() pross.c Solution In the c programming the shell commands can't be executed directly, but there are several other options to get implemented. 1. Do not use the shell , but bypass the shell and run the commands driectly with specified program.Many of the basic utilities can be accessed easily enough and system calls are available for system programming tasks.You need to use pipe() ,fork () and exec(). 2. Use system() to run the command if input and output are not important. 3.use poopen () if control on either input or output is needed. 4. run the shell as a coprocess. If we select to bypass the shell, it can be bit easier to have buffered.
- 2. STDIO functions are available on a file decsriptor with fdopen- associate a sream with a file descritor FILE *fdopen(int fd , const char *mode); after this call, STDIO buffered I/O and standard I/O function such as scanf() and print f() can be used on fd. system- run shell command int system(const char *command); poopen- open to/from shell FILE *POPEN(const char *command, const char * type); int pclose (FILE *stream); FILE *fp; char *command; fp=popen(command,"r"); fscanf(fp,....); fclose(fp); fp=open(command ,"w"); fprintf(fp,.....); fclose(fp); The shell can be forked off as a child of the program and then commands can be both sent to it and the results can be read. More generally any other program could be run this way. There are number of problems with this approach. 1. The practical problem of keeping the process in sync. For instance can you recognizing when the coprocess has finished responding to given request. 2. the shell is receiving its input through a pipe and not through a terminal , it uses file not line buffering, It will not receive input until the buffer is full. some solutions to this problems are
- 3. override the standard isatty by dynamically linking in a version that always returns true.this will require altering the environment before calling the child coprocess, so that the child process dynamic load library path includes the revised ispatty.