$//$ redirect$\_$child.c: starts a child process which will print into a

$//$ file instead of onto the screen. Uses dup$2(),$ fork$(),$ and wait$()$

$//$ for this.

$//$

$//$ COMPLETE this code by filling in the TODO$/???$ items

#include

#include

#include

#include

#include

int main$($int argc, char $*$argv$[])\{$

if$($argc $<2)\{//$ check for at least $1$ command line arg

printf$("$usage: $\%$s

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

return $1$;

$\}$

char $*$output$\_$file $=$ argv$[1]$; $//$ output file that child process will print into

char $*$child$\_$argv$[]=\{"$wc$",$"nums.txt$",$NULL$\}$; $//$ child command$/$argumnets to execute; redirect output to file above

printf$("$Removing file $\text{'}\%$s$\text{'}$ prior to run via a subshell

$",$

output$\_$file$)$;

$//$ Create a string command and run it in a subshell; the 'system$()\text{'}$

$//$ command is a convenient way to fork$()+$exec$()+$wait$()$ a child

$//$ with blocking semantics

char command$[128]$;

sprintf$($command$,"$rm $-$f $\%$s$",$output$\_$file$)$;

system$($command$)$;

printf$("$Creating a child to do $\text{'}\%$s$\text{'}$

$",$ child$\_$argv$[0])$;

$//$ TODO: Spawn a child process

$???=???$;

$//$ CHILD CODE

$//$ TODO: Conditional for child only

if$(???)\{$

printf$("$Child redirecting output to $\text{'}\%$s$\text{'},$ then exec$()\text{'}$ing

$",$

output$\_$file$)$;

$//$ TODO: Open output$\_$file for writing, same options as in switch$\_$stdout.c

int out$\_$fd $=???$

$//$ TODO: Copy out$\_$fd to standard output FD table entry

d$???(???)$;

$//$ TODO: Execute the command in child$\_$argv$[]$ replacing this process

exec??$(???)$;

printf$("$exec$()$ seems to have failed...

$")$; $//$ should not reach this

exit$(1)$;

$\}$

$//$ PARENT CODE

printf$("$Parent waiting for child to complete

$")$;

int status; $//$ used to check return code of child

$//$ TODO: Block until child is finished and check the output

$????(???)$;

$//$ TODO: check if the child exited properly using wait macros

if$(???)\{$

$//$ TODO: extract exit$/$return code of child process using wait macros

int retcode $=???$;

printf$("$Child complete, return code $\%$d

$",$retcode$)$;

$\}$

else$\{//$ Child did not complete properly

printf$("$Child terminated abnormally

$")$;

exit$(1)$;

$\}$

printf$("$Showing output of $\text{'}\%$s$\text{'}$ via 'cat' command

$",$

output$\_$file$)$;

$//$ Create another command to show the contents of output$\_$file; use

$//$ system$()$ to 'cat' the contents to the screen

sprintf$($command$,$ "cat $\%$s$",$ output$\_$file$)$;

system$($command$)$;

return $0$;

$\}$