Homework 3, DASH (or whatever you wish).

Short Description:

Goals

• Written a program that uses fork, exec, dup, wait, ...
• You will probably get better with an array of pointers as well :), but that is a side effect.

Formal Description

For 1/4 credit your program should

1. prompt
2. read the command line given
3. execute the command, including passing arguments
4. wait for the command to exit
5. Return to step 1.

dash -> ls -alrt /
total 24
drwxr-xr-x.   1 root root    0 Jan 23  2024 srv
lrwxrwxrwx.   1 root root    8 Jan 23  2024 sbin -> usr/sbin
drwxr-xr-x.   1 root root    0 Jan 23  2024 mnt
drwxr-xr-x.   1 root root    0 Jan 23  2024 media
...
dash -> 

For 1/4 credit you should support I/O redirection to a file.

• If the command contains a >, redirect the output to the value immediately following the >.
  • This file should be created with rw permissions for the user.
  • It should be truncated if it has data in it.
• If the command contains a <, redirect the input from the value immediately following the <

dash -> cat < dash.cpp > newDash.cpp -n
dash -> more newDash.cpp
     1  #include <iostream>
     2  #include <sys/wait.h>
     ...
dash-> 

For 1/4 credit support pipes between processes

• 1/8 for two commands: cmd1 args | cmd2 args
• 1/8 for more than two commands: cmd1 args | cmd 2 args | ... | cmdn args

dash -> ls -a | sort -d | grep cpp
dash.cpp
two.cpp
dash-> 

For the final 1/4 credit make sure that both i/o redirection and pipes work.

• But i only on the first command
• And o only on the last command.

dash -> grep -o '[[:alpha:]]*' < dash.cpp | sort -n | uniq > words
dash -> cat words
ParseCmd
arg
args
auto
back
...
dash -> 

Notes:

• I only wrote part of this so you are on your own for part.
• You may use vectors or any other item from the standard library.
• I needed to pass an array of characters by reference:
  • void ParseCmd(string cmd, char ** & args,...
  • But no memory leaks!
• I would build a struct to hold a command to be executed
  • The command
  • A vector of the arguments, or perhaps a char** of the arguments
  • A flag indicating if output is redirected
  • A file name to redirect output to
  • A flag indicating if input is redirected
  • A file name to redirect input from
• I think I would build a vector of these then, indicating that they should be connected with a pipe.
• Oh and you probably need to catch the cd command and do that in the shell.
  • Look at chdir, but again only in the shell.
  • If you change the directory in a subshell, it will not change the directory in the parent shell, which is what you want.

Required Files

Submission