#include "csapp.h$"$#define MAXARGS$128$void eval$($char$*$cmdline$)$;$$int parseline$($char $*$buf$,$ char $**$argv$)$;$$int builtin$\_$command$($char $**$argv$)$;$$int main$()\{$ char cmdline$[$MAXLINE$]$; $$ while $(1)\{$ printf$(">")$;$$ Fgets$($cmdline$,$ MAXLINE, stdin$)$;$$ if $($feof$($stdin$))$ exit$(0)$;$$ eval$($cmdline$)$;$\}\}$void eval$($char $*$cmdline$)\{$ char $*$argv$[$MAXARGS$]$;$$ char buf$[$MAXLINE$]$;$$

$$ int bg;$$ pid$\_$t pid;$$ strcpy$($buf$,$ cmdline$)$;$$ bg $=$ parseline$($buf$,$ argv$)$;$$ if $($argv$[0]==$ NULL$)$ return;$$ if $(!$builtin$\_$command$($argv$))\{$ if $(($pid $=$ Fork$())==0)\{$ if $($execve$($argv$[0],$ argv, environ$)<0)\{$ printf$("\%$s: Command not found.

$",$ argv$[0])$;$$ exit$(0)$;$\}\}$ if $(!$bg$)\{$ int status;$$ if $($waitpid$($pid$,$ &status, $0)<0)$ unix$\_$error$("$waitfg: waitpid error"$)$;$\}$ else$$ printf$("\%$d $\%$s$",$ pid, cmdline$)$;$\}$ return;$\}$int builtin$\_$command$($char $**$argv$)\{$ if $(!$strcmp$($argv$[0],$ "quit"$))$ exit$(0)$;$$ if $(!$strcmp$($argv$[0],"$&$"))$ return $1$;$$ return $0$;$\}$int parseline$($char $*$buf$,$ char $**$argv$)\{$ char $*$delim;$$ int argc;$$ int bg;$$ buf$[$strlen$($buf$)-1]=\text{'}\text{'}$; $$ while $(*$buf && $(*$buf $==\text{'}\text{'}))$ buf$++$;$$ argc $=0$;$$ while $(($delim $=$ strchr$($buf$,\text{'}\text{'})))\{$ argv$[$argc$++]=$ buf;$*$delim $=\text{'}\backslash 0\text{'}$;$$ buf $=$ delim $+1$;$$ while $(*$buf && $(*$buf $==\text{'}\text{'}))$ buf$++$;$\}$ argv$[$argc$]=$ NULL;$$ if $($argc $==0)$ return $1$;$$ if $(($bg $=(*$argv$[$argc$-1]==\text{'}$&$\text{'}))!=0)$ argv$[--$argc$]=$ NULL;$$ return bg;$\}$

edit this code so that Your new version must maintain variables using a local array of strings abc$=$xyz$.$ It should not rely on the real shell to keep these strings. Which means that at the top of it there must be a declaration like char $*$vars$[10]$ to have an array that will contain up to $($for example$)10$ strings in the form abc$=$xyz$.$ When the user types a command like set path$=/$home$/$ck$47/$progs your shell should find an empty element in local array vars$[],$ call malloc$()$ and store the string there. When the user types a command to run a program from the disk, say $>$ test arg$1$ arg$2$ your shell should use execve$()$ to find the program in the current directory. If the program in not found, execve$()$ returns error and your shell should insert the PATH value before the filename $($by creating a new string and concatenating$)$ and call execve$()$ with that new string. So$,$ in the above example, either program test is executed or program $/$home$/$ck$47/$progs$/$test is executed.