Instructions

Enhance your code from the ps$3-$simple shell with I$/$O redirection assignment to include the ability to send the output from one program as input to another program. This functionality is supported by a mechanism called a pipe.

SimpleShell.cpp:

$//$ Including header file path #include $"../$include$/$SimpleShell$.$h$"//$ Including all necessary libraries #include #include #include #include #include #include #include #include #include #include using namespace std; void SimpleShell::execute$($const vector& argv$)\{//$ Checking if there are no commands to execute if$($argv$.$empty$())\{$ cerr $<<$ "Error: No command to execute" $<<$ endl; return; $\}//$ Preventing execution of the shell itself if$($argv$[0]=="./$bin$/$SimpleShell$")\{$ cerr $<<$ "Error: Cannot execute the shell itself." $<<$ endl; return; $\}//$ Variables to store the status of the child process and the child process ID$,$ respectively int status; pid$\_$t child; $//$ Creating a new process child $=$ fork$()$; if$($child $>0)\{//$ Waiting for the child process to finish waitpid$($child$,$ &status, $0)$; $\}$ else if$($child $==0)\{//$ Child process if$($argv$.$empty$())\{$ cerr $<<$ "Error: No command to execute" $<<$ endl; $\_$exit$(1)$; $\}$ vector args; $//$ Vector to hold command arguments string input$\_$file; $//$ String to hold input file name string output$\_$file; $//$ String to hold output file name $//$ Parsing the command line arguments for$($size$\_$t i $=0$; i $<$ argv.size$()$; $++$i$)\{$ if$($argv$[$i$]=="<")\{//$ Input redirection if$($i $+1<$ argv.size$())\{$ input$\_$file $=$ argv$[$i $+1]$; $//$ Getting the input file name $++$i; $//$ Skipping the file name in the next iteration $\}$ else $\{$ cerr $<<$ "Error: No input file specified." $<<$ endl; $\_$exit$(1)$; $\}\}$ else if $($argv$[$i$]==">")\{//$ Output redirection if$($i $+1<$ argv.size$())\{$ output$\_$file $=$ argv$[$i $+1]$; $//$ Getting the output file $++$i; $//$ Skipping the file name in the next iteration $\}$ else $\{$ cerr $<<$ "Error: No output file specified." $<<$ endl; $\_$exit$(1)$; $\}\}$ else $\{//$ Adding command arguments to vector args.push$\_$back$($argv$[$i$])$; $\}\}//$ Handling input redirection if$(!$input$\_$file.empty$())\{$ int fd$\_$in $=$ open$($input$\_$file.c$\_$str$(),$ O$\_$RDONLY$)$; $//$ Opening the input file if$($fd$\_$in $<0)\{$ perror$("$Error opening input file"$)$; $\_$exit$(1)$; $\}$ dup$2($fd$\_$in$,$ STDIN$\_$FILENO$)$; $//$ Redirecting standard input to the input file close$($fd$\_$in$)$; $//$ Closing the input file descriptor $\}//$ Handling output redirection if$(!$output$\_$file.empty$())\{$ int fd$\_$out $=$ open$($output$\_$file.c$\_$str$(),$ O$\_$WRONLY $|$ O$\_$CREAT $|$ O$\_$TRUNC, S$\_$IRUSR $|$ S$\_$IWUSR$)$; $//$ Opening the output file if$($fd$\_$out $<0)\{$ perror$("$Error opening output file"$)$; $\_$exit$(1)$; $\}$ dup$2($fd$\_$out, STDOUT$\_$FILENO$)$; $//$ Redirecting the standard output to the output file close$($fd$\_$out$)$; $//$ Close the output file descriptor $\}//$ Vector to hold strings for execvp vector exec$\_$args; for$($const auto& arg : args$)\{$ exec$\_$args.push$\_$back$($arg$.$c$\_$str$())$; $//$ Convert each string to const char$*\}$ exec$\_$args.push$\_$back$($nullptr$)$; $//$ Terminate the argument list $//$ Execute the command using execvp if$($execvp$($exec$\_$args$[0],$ const$\_$cast$($exec$\_$args.data$()))==-1)\{$ perror$("$execvp failed"$)$; $\_$exit$(1)$; $\}\}//$ Handling fork failure else $\{$ perror$("$fork failed"$)$; exit$(1)$; $\}\}//$ Method to parse a line of input into tokens based on a given delimeter void SimpleShell::parse$($const string& line, vector& tokens, const string& delimeter$)\{$ size$\_$t start $=0$; $//$ Starting position for each substring search size$\_$t end $=0$; $//$ Ending position for substring search $//$ Loop to find and extract tokens separated by a delimiter while$(($end $=$ line.find$($delimeter$,$ start$))!=$ string::npos$)\{$ if$($end $!=$ start$)\{$ tokens.push$\_$back$($line$.$substr$($start$,$ end $-$ start$))$; $//$ Add token to the vector $\}$ start $=$ end $+$ delimeter.length$()$; $//$ Move start position to the next character $\}//$ Add the last token if there is any remaining text if$($start $<$ line.length$())\{$ tokens.push$\_$back$($line$.$substr$($start$))$; $\}\}//$ Main loop for running the shell void SimpleSh