Modify that minishell.c to do the following:

$1.$ put commands ended by an $$&$$ into background mode and report when they finish.

$2.$ properly interpret the shell cd command

$3.$ include an appropriate perror statement after each and every system call.

$4.$ fix the minishell so that if the exec system call fails, the child process is correctly terminated.

#include

#include

#include

#include

#include

#include

#include

#define NV $20/*$ max number of command tokens $*/$

#define NL $100/*$ input buffer size $*/$

char line$[$NL$]$; $/*$ command input buffer $*/$

$/*$

shell prompt

$*/$

prompt$($void$)$

$\{$

fprintf$($stdout$,"$

msh$>")$;

fflush$($stdout$)$;

$\}$

main$($int argk, char $*$argv$[],$ char $*$envp$[])$

$/*$ argk $-$ number of arguments $*/$

$/*$ argv $-$ argument vector from command line $*/$

$/*$ envp $-$ environment pointer $*/$

$\{$

int frkRtnVal; $/*$ value returned by fork sys call $*/$

int wpid; $/*$ value returned by wait $*/$

char $*$v$[$NV$]$; $/*$ array of pointers to command line tokens $*/$

char $*$sep $="\backslash$t

$"$;$/*$ command line token separators $*/$

int i; $/*$ parse index $*/$

$/*$ prompt for and process one command line at a time $*/$

while $(1)\{/*$ do Forever $*/$

prompt$()$;

fgets$($line$,$ NL$,$ stdin$)$;

fflush$($stdin$)$;

if $($feof$($stdin$))\{/*$ non$-$zero on EOF $*/$

fprintf$($stderr$,$ "EOF pid $\%$d feof $\%$d ferror $\%$d

$",$ getpid$(),$

feof$($stdin$),$ ferror$($stdin$))$;

exit$(0)$;

$\}$

if $($line$[0]==\text{'}$#$\text{'}||$ line$[0]==\text{'}$

$\text{'}||$ line$[0]==\text{'}\backslash 000\text{'})$

continue; $/*$ to prompt $*/$

v$[0]=$ strtok$($line$,$ sep$)$;

for $($i $=1$; i $<$ NV; i$++)\{$

v$[$i$]=$ strtok$($NULL$,$ sep$)$;

if $($v$[$i$]==$ NULL$)$

break;

$\}$

$/*$ assert i is number of tokens $+1*/$

$/*$ fork a child process to exec the command in v$[0]*/$

switch $($frkRtnVal $=$ fork$())\{$

case $-1$: $/*$ fork returns error to parent process $*/$

$\{$

break;

$\}$

case $0$: $/*$ code executed only by child process $*/$

$\{$

execvp$($v$[0],$ v$)$;

$\}$

default: $/*$ code executed only by parent process $*/$

$\{$

wpid $=$ wait$(0)$;

printf$("\%$s done

$",$ v$[0])$;

break;

$\}$

$\}/*$ switch $*/$

$\}/*$ while $*/$

$\}/*$ main $*/$