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smallsh.c
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smallsh.c
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// smallsh
// By George Hill
// CS 344
// 2020-05-10
// Implements a simple bash-like shell with support for (a) three built-in
// commands (status, cd, and exit), (b) file redirection (with < and >),
// (c) background processes (with &), and (d) otherwise generally calling
// GNU/Linux executables. Ignores Ctrl-C and interprets Ctrl-Z as toggling
// on and off a "foreground-only" mode in which "&" is ignored.
// 80 Columns: /////////////////////////////////////////////////////////////////
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>
#define TRUE 1
#define FALSE 0
#define MAX_STRING_LENGTH 2048
#define MAX_COMMAND_ARRAY_SIZE 518
// We will have an array of strings. It will have one string for the command,
// 512 strings for arguments, four strings for redirection symbols and their
// files, and one final string for commands that should be run in the background.
// That adds up to 518 strings.
#define MAX_DIGITS_IN_PROCESS_ID 10 // This is a guess.
#define STATUS_REPORT_MAX_LENGTH 100
#define EXIT_VALUE 1
#define SIGNAL_RECEIVED 0
// The statusType variable in main() will track how the last foreground process
// terminated. If it exited normally, the statusType variable will have the
// value EXIT_VALUE. If it exited because of a signal, it will have the value
// SIGNAL_RECEIVED.
#define COMMAND_AND_ARGUMENT_DELIMITER " " // Must use double-quotes.
// We will use this to separate commands and arguments from each other.
#define PROCESS_NUMBER_SYMBOL '$' // Must use single-quotes because used with
// character comparison.
// We will use this to search for "$$" in the user's input.
#define COMMENT_SYMBOL '#' // Must use single-quotes.
// We will use this to identify comment lines.
#define BACKGROUND_SYMBOL "&" // Must use double-quotes because used with
// strcmp().
// We will use this to identify commands that need to run in the background.
#define REDIRECT_INPUT "<" // Must use double-quotes.
#define REDIRECT_OUTPUT ">" // Must use double-quotes.
// We will use these to identify commands that need file redirection.
#define DEV_NULL "/dev/null"
// We will use this with certain background processes.
#define EXIT_COMMAND "exit"
#define STATUS_COMMAND "status"
#define CD_COMMAND "cd"
// These are the three built-in commands.
struct runningProcess // Will store process IDs of running proceses in a
// linked list.
{
int processID;
struct runningProcess* next;
};
int usingBackgroundIsPossible = TRUE;
int receivedSigtstp = FALSE;
int weAreWaitingForForegroundProcessToStop = FALSE;
// As far as I can tell, we need to use global variables so that the shell
// can catch SIGTSTP signal _during execution of a foreground process_ and make
// a plan to act on that signal only after the termination of the foreground
// process. That is to say, I don't know that we have any other way to pass the
// function variables to manipulate.
// The next two functions will be used throughout the rest of the program
// to safely generate output:
void outputStringWithNoNewline(char* text)
{
printf("%s", text);
fflush(stdout);
}
void outputStringWithANewline(char* text)
{
printf("%s\n", text);
fflush(stdout);
}
// This function toggles our state between the normal mode and the foreground-
// only mode:
void implementSigtstpLogic()
{
if (usingBackgroundIsPossible == TRUE)
{
usingBackgroundIsPossible = FALSE;
char* message =
"\nEntering foreground-only mode (& is now ignored)\n";
write(STDOUT_FILENO, message, 50);
}
else
{
usingBackgroundIsPossible = TRUE;
char* message = "\nExiting foreground-only mode\n";
write(STDOUT_FILENO, message, 30);
}
}
// This function will be called when our (parent) shell process receives
// a SIGTSTP:
void dealWithSigtstp(int signo)
{
if (weAreWaitingForForegroundProcessToStop == FALSE)
{
// We aren't blocked at waitpid(), so we are (probably) at the
// command-line prompt, so we should act on SIGTSTP right away.
implementSigtstpLogic();
}
else
{
// We _are_ blocked at waitpid(), so we hold off on doing anything
// about SIGTSTP until the foreground process terminates. However,
// in order to do that, we need to update this global variable so
// that the work can be done when we are done being blocked at
// waitpid().
receivedSigtstp = TRUE;
}
return;
}
// This function removes the given pid from the linked list that contains
// the pid's of background processes. As noted below, writing it was hard.
void forget(int processID, struct runningProcess** listOfProcesses)
{
struct runningProcess* current = *listOfProcesses;
// By dereferencing the pointer to a pointer, we end up with "current"
// being a pointer that has the same value as "listOfProcesses" in main().
// I think.
struct runningProcess* previous = NULL;
// Iterate over the linked list until locating the link that contains the
// pid that we seek:
while (current->processID != processID)
{
previous = current;
current = current->next;
}
if (previous != NULL)
{
// Remove "current" from the linked list:
previous->next = current->next;
}
else
{
// "previous" is still NULL, which means that we found the pid in the
// very first link, which means that we need to set the head of the
// linked list to point to the second element in the list (or to NULL,
// which will be the value of "current->next" if there is no second
// link).
*listOfProcesses = current->next;
}
free(current);
return;
}
// This function checks to see if the process with the given pid has finished.
// If it has, this function calls another function to remove that pid from the
// linked list of background processes. As noted below, writing this was
// difficult.
void checkStatusOfProcess
(
int processID,
struct runningProcess** listOfProcesses
)
{
// printf("checkStatusOfProcess(%d)\n", processID);
int exitedOrNot = -5;
int childExitMethod = -5;
int statusValue = -5;
char statusReport[STATUS_REPORT_MAX_LENGTH];
exitedOrNot = waitpid(processID, &childExitMethod, WNOHANG);
if (exitedOrNot == 0) {
return;
}
if (WIFEXITED(childExitMethod) != 0)
{
// The process exited by exit(0), exit(1), return 0, etc.
statusValue = WEXITSTATUS(childExitMethod);
sprintf
(
statusReport,
"background pid %d is done: exit value %d",
processID,
statusValue
);
outputStringWithANewline(statusReport);
forget(processID, listOfProcesses);
}
else if (WIFSIGNALED(childExitMethod) != 0)
{
// The process exited because of an uncaught signal.
statusValue = WTERMSIG(childExitMethod);
sprintf
(
statusReport,
"background pid %d is done: terminated by signal %d",
processID,
statusValue
);
outputStringWithANewline(statusReport);
forget(processID, listOfProcesses);
}
return;
}
// This function iterates over a linked list of process IDs from background
// processes. For each process ID encountered, it calls a separate function
// to see if that process has exited yet. Because this is a linked list using
// pointers to pointers, writing it was hard, and so I'm leaving in the
// printf() calls used for debugging (although they are commented out).
void checkForFinishedBackgroundProcesses
(
struct runningProcess** listOfProcesses
)
{
struct runningProcess* current = *listOfProcesses;
// By dereferencing the pointer to a pointer, we end up with "current"
// being a pointer that has the same value as "listOfProcesses" in main().
// I think.
struct runningProcess* temp = NULL;
// printf("checkForFinishedBackgroundProcesses, %p\n", *listOfProcesses);
// Iterate over each element in the linked list. If there are no links in
// the list, then "current" will equal NULL and we won't look at anything.
// If there are links in the list, then "current" will equal NULL when it
// finally reaches the last link.
while (current != NULL)
{
temp = current;
current = current->next; // This has to be before the next line because
// the next line might lead to a forget() call.
// printf("current: %p\n", current);
checkStatusOfProcess(temp->processID, listOfProcesses);
}
return;
}
// Output prompt, get line of user input, and parse each word of that input
// into an array, noting the total number of array elements used:
void getCommandArray
(
char commandArray[MAX_COMMAND_ARRAY_SIZE][MAX_STRING_LENGTH],
int* arrayElementsUsed
)
{
// Sample code for using getline was provided by the instructor at:
// http://web.engr.oregonstate.edu/~brewsteb/CS344Slides/2.4%20File%20Access%20in%20C.pdf
// And at:
// http://web.engr.oregonstate.edu/~brewsteb/THCodeRepository/userinput_adv.c
int numCharsEntered = -5; // Will hold the number of characters entered.
size_t bufferSize = 0; // Will hold how large the allocated buffer is.
char* lineEntered = NULL; // Will point to a buffer allocated by getline()
// that holds the entered string + \n + \0.
while(TRUE)
{
outputStringWithNoNewline(": "); // Output prompt.
numCharsEntered = getline(&lineEntered, &bufferSize, stdin);
// Get a line from the user.
if (numCharsEntered == -1)
{
// We got an error, probably because someone sent a SIGTSTP.
clearerr(stdin);
}
else
{
break;
}
}
lineEntered[numCharsEntered - 1] = 0; // Turn ending \n into a \0.
char* token = NULL;
int index = 0;
token = strtok(lineEntered, COMMAND_AND_ARGUMENT_DELIMITER);
while (token != NULL)
{
strcpy(commandArray[index], token);
index++;
token = strtok(NULL, COMMAND_AND_ARGUMENT_DELIMITER);
}
free(lineEntered);
*arrayElementsUsed = index;
return;
}
// Replace each instance of "$$" with the process ID:
void replaceDoubleDollarSigns
(
char commandArray[MAX_COMMAND_ARRAY_SIZE][MAX_STRING_LENGTH],
int arrayElementsUsed
)
{
// Iterate over each word in the array:
int i;
for (i = 0; i < arrayElementsUsed; i++) {
int currentWordHasMadeItThrough = FALSE;
// The current world will have "made it through" when it can go through
// the entire inner iterator without triggering a substitution from
// "$$" to "<pid>". It's not enough to run it through once, because
// we might have multiple "$$" substrings. After hitting a "$$"
// substring, we'll break out of the inner iterator and recheck the
// string from the very top.
while (currentWordHasMadeItThrough == FALSE)
{
int wordLength = strlen(commandArray[i]);
int weMadeAChange = FALSE;
// Iterate over each character in the current word:
int j;
for (j = 0; j < wordLength - 1; j++)
{
char firstChar = commandArray[i][j];
char secondChar = commandArray[i][j + 1];
if (firstChar == PROCESS_NUMBER_SYMBOL &&
secondChar == PROCESS_NUMBER_SYMBOL)
{
// We hit a "$$" substring starting at character j.
char tempWord[MAX_STRING_LENGTH + MAX_DIGITS_IN_PROCESS_ID];
// Copy in the characters that come before the first "$":
int k;
for (k = 0; k < j; k++)
{
tempWord[k] = commandArray[i][k];
}
// Get the process id into a string:
// https://stackoverflow.com/questions/53230155/converting-pid-t-to-string
int pid = getpid();
char tempPidString[MAX_DIGITS_IN_PROCESS_ID];
sprintf(tempPidString, "%d", pid);
// Iterate over the process ID string, copying it in to the
// temporary word:
int tempPidStringLength = strlen(tempPidString);
for (k = 0; k < tempPidStringLength; k++)
{
tempWord[j + k] = tempPidString[k];
}
// Copy in the characters that come after the "$$"
// substring.
int m = 0;
for (k = j + 2; k < wordLength; k++)
{
tempWord[j + tempPidStringLength + m] =
commandArray[i][k];
m++;
}
// Make sure to mark the end of the temporary string:
tempWord[j + tempPidStringLength + m] = 0;
strcpy(commandArray[i], tempWord);
weMadeAChange = TRUE;
break; // Break out of the for-j loop.
}
}
if (weMadeAChange == FALSE)
{
currentWordHasMadeItThrough = TRUE;
}
}
}
return;
}
// This function helps implemnent the "exit" built-in command. It needs to
// terminate any background processes. This function is similar to
// checkForFinishedBackgroundProcesses().
void prepForExit(struct runningProcess** listOfProcesses)
{
struct runningProcess* current = *listOfProcesses;
// By dereferencing the pointer to a pointer, we end up with "current"
// being a pointer that has the same value as "listOfProcesses" in main().
// I think.
struct runningProcess* temp = NULL;
// Iterate over each element in the linked list. If there are no links in
// the list, then "current" will equal NULL and we won't look at anything.
// If there are links in the list, then "current" will equal NULL when it
// finally reaches the last link.
while (current != NULL)
{
temp = current;
current = current->next;
kill(temp->processID, SIGKILL);
// It seems to me that we should output a message noting that the
// background process was terminated, so I am including the following:
int childExitMethod;
int statusValue;
char statusReport[STATUS_REPORT_MAX_LENGTH];
waitpid(temp->processID, &childExitMethod, 0);
if (WIFEXITED(childExitMethod) != 0)
{
// The process exited by exit(0), exit(1), return 0, etc.
statusValue = WEXITSTATUS(childExitMethod);
sprintf
(
statusReport,
"background pid %d is done: exit value %d",
temp->processID,
statusValue
);
outputStringWithANewline(statusReport);
forget(temp->processID, listOfProcesses);
}
else if (WIFSIGNALED(childExitMethod) != 0)
{
// The process exited because of an uncaught signal.
statusValue = WTERMSIG(childExitMethod);
sprintf
(
statusReport,
"background pid %d is done: terminated by signal %d",
temp->processID,
statusValue
);
outputStringWithANewline(statusReport);
forget(temp->processID, listOfProcesses);
}
}
return;
}
// This function implements the "status" built-in command:
void outputStatus(int statusType, int statusValue)
{
if (statusType == EXIT_VALUE)
{
outputStringWithNoNewline("exit value ");
}
else
{
outputStringWithNoNewline("terminated by signal ");
}
char valueOrSignal[5];
sprintf(valueOrSignal, "%d", statusValue);
outputStringWithANewline(valueOrSignal);
return;
}
// This function implements the "cd" built-in command:
void changeDirectory(char parameter[MAX_STRING_LENGTH])
{
const char* homePath = getenv("HOME");
// http://www0.cs.ucl.ac.uk/staff/W.Langdon/getenv/
if (strlen(parameter) == 0 || strcmp(parameter, "~") == 0)
// Strangely, chdir() wouldn't respond to having a "~" string as
// its parameter. It ignored it. In order to make "cd ~" work as
// expected, it is necessary to test the parameter for "~" and treat it
// as if the user entered just "cd".
{
chdir(homePath);
}
else
{
chdir(parameter);
}
return;
}
// This function adds background-command pids to a linked list. It was
// extremely hard to debug, so I'm leaving my debugging printf() statements in
// (although they are commented out).
void remember(struct runningProcess** listOfProcesses, int processToRemember)
{
// printf
// (
// "remember(%p, %d) and *listOfProcesses = %p\n",
// listOfProcesses,
// processToRemember,
// *listOfProcesses
// );
if (*listOfProcesses == NULL) {
// We don't have any links yet in our linked list, so we have to create
// one:
// printf("Going to make first link.\n");
*listOfProcesses =
(struct runningProcess*)malloc(sizeof(struct runningProcess));
(*listOfProcesses)->processID = processToRemember;
(*listOfProcesses)->next = NULL;
} else {
// We already have at least one link in our linked list of processes to
// remember, so we need to add the current one at the end:
// printf("Going to make an additional link.\n");
struct runningProcess* current = (*listOfProcesses)->next;
struct runningProcess* previous = *listOfProcesses;
// printf("ccurent: %p\n", current);
while (current != NULL) {
previous = current;
current = current->next;
}
// printf("cccurent: %p\n", current);
// Having reached the end, we create another link. However, it's
// not enough to know "current", because current == NULL, and that
// doesn't help us add a link. We need to know "previous" so that we
// can add our link to previous->next:
previous->next =
(struct runningProcess*)malloc(sizeof(struct runningProcess));
previous->next->processID = processToRemember;
previous->next->next = NULL;
}
return;
}
// This function evalutes the command array to see if there is a need for
// input/output redirection or running in the background. It then actually
// executes the command by using fork() and execvp(). It also deals with the
// aftermath of executing a command by waiting for foreground commands (and
// noting their manner of termination) and by adding background-command pids
// to a linked list.
void executeCommand
(
char commandArray[MAX_COMMAND_ARRAY_SIZE][MAX_STRING_LENGTH],
int arrayElementsUsed,
int* statusType,
int* statusValue,
int* usingBackgroundIsPossible,
struct runningProcess** listOfProcesses,
struct sigaction* originalSigintAction
)
{
int actuallyRunInBackground = FALSE;
char fileForInputRedirection[MAX_STRING_LENGTH] = "";
char fileForOutputRedirection[MAX_STRING_LENGTH] = "";
// See if there is a BACKGROUND_SYMBOL as the last element in the command
// array, and if so deal with it:
if (strcmp(commandArray[arrayElementsUsed - 1], BACKGROUND_SYMBOL) == 0)
{
if (*usingBackgroundIsPossible == TRUE)
{
actuallyRunInBackground = TRUE;
}
arrayElementsUsed--;
}
// Check the last two arguments to see if we might be redirecting input or
// output:
int needToCheckOneMoreTime = FALSE;
if (strcmp(commandArray[arrayElementsUsed - 2], REDIRECT_INPUT) == 0)
{
strcpy(fileForInputRedirection, commandArray[arrayElementsUsed - 1]);
arrayElementsUsed = arrayElementsUsed - 2;
needToCheckOneMoreTime = TRUE;
}
else if (strcmp(commandArray[arrayElementsUsed - 2], REDIRECT_OUTPUT) == 0)
{
strcpy(fileForOutputRedirection, commandArray[arrayElementsUsed - 1]);
arrayElementsUsed = arrayElementsUsed - 2;
needToCheckOneMoreTime = TRUE;
}
// If the last two elements indicated redirection, then we also need to
// check the two elements before them:
if (needToCheckOneMoreTime == TRUE)
{
if (strcmp(commandArray[arrayElementsUsed - 2], REDIRECT_INPUT) == 0)
{
strcpy
(
fileForInputRedirection,
commandArray[arrayElementsUsed - 1]
);
arrayElementsUsed = arrayElementsUsed - 2;
}
else if
(
strcmp(commandArray[arrayElementsUsed - 2], REDIRECT_OUTPUT) == 0
)
{
strcpy
(
fileForOutputRedirection,
commandArray[arrayElementsUsed - 1]
);
arrayElementsUsed = arrayElementsUsed - 2;
}
}
// Now we need to take commandArray and put it in a form that we can send
// to execvp():
char* commandArgs[arrayElementsUsed];
int i;
for (i = 0; i < arrayElementsUsed; i++)
{
commandArgs[i] = calloc(MAX_STRING_LENGTH, sizeof(char));
strcpy(commandArgs[i], commandArray[i]);
}
commandArgs[arrayElementsUsed] = NULL;
// NOW WE FORK() AND EXECVP() !!!
// Template for forking comes from instructor at:
// http://web.engr.oregonstate.edu/~brewsteb/CS344Slides/3.1%20Processes.pdf
pid_t spawnPid = -5;
int childExitMethod = -5;
spawnPid = fork();
if (spawnPid == -1) // Error!
{
perror("Error when attempting to fork!\n");
exit(1);
}
else if (spawnPid == 0) // We are in the child process!
{
// If the file is going to run in the background, then we will need to
// set up input and output redirection (unless the user has already
// specified such redirection):
if (actuallyRunInBackground == TRUE)
{
if (strcmp(fileForInputRedirection, "") == 0)
{
strcpy(fileForInputRedirection, DEV_NULL);
}
if (strcmp(fileForOutputRedirection, "") == 0)
{
strcpy(fileForOutputRedirection, DEV_NULL);
}
}
// Now actually set up input redirection, if necessary:
if (strcmp(fileForInputRedirection, "") != 0)
{
// Code for file redirection derived from professor's examples at:
// http://web.engr.oregonstate.edu/~brewsteb/CS344Slides/3.4%20More%20UNIX%20IO.pdf
int sourceFD = open(fileForInputRedirection, O_RDONLY);
if (sourceFD == -1) {
perror("Error when opening file for input redirection!");
// printf("cannot open %s for input", fileForInputRedirection);
exit(1);
}
int result = dup2(sourceFD, 0);
if (result == -1)
{
perror("Error when initiating input redirection!");
exit(1);
}
}
// And actualy set up output redirection, if necessary:
if (strcmp(fileForOutputRedirection, "") != 0)
{
int targetFD = open
(
fileForOutputRedirection,
O_WRONLY | O_CREAT | O_TRUNC,
0644
);
if (targetFD == -1) {
perror("Error when opening file for output redirection!");
// printf("cannot open %s for output", fileForOutputRedirection);
exit(1);
}
int result = dup2(targetFD, 1);
if (result == -1)
{
perror("Error when initiating output redirection!");
exit(1);
}
}
// If the command is going to be run in the _foreground_, we need to
// set sigaction(SIGINT) back to its original behavior (the behavior
// it had before we set things to ignore SIGINT):
if (actuallyRunInBackground == FALSE)
{
sigaction(SIGINT, originalSigintAction, NULL);
}
// Whether this is going to be a foreground process or a background
// process--either way--we need to set this child process to ignore
// SIGTSTP:
struct sigaction ignoreAction = {{0}};
ignoreAction.sa_handler = SIG_IGN;
sigaction(SIGTSTP, &ignoreAction, NULL);
// And finally we're ready to execvp():
// Pattern for execvp() comes from instructor at:
// http://web.engr.oregonstate.edu/~brewsteb/CS344Slides/3.1%20Processes.pdf
if (execvp(*commandArgs, commandArgs) < 0)
{
perror("Error when attempting to execute command!");
exit(1);
}
}
// Otherwise, we are still in the parent process!
if (actuallyRunInBackground == FALSE)
{
// We're running the command in the foreground, so we have to wait
// for it to terminate:
// We have to make sure that these globe variables are set correctly
// so that we can deal with it if a SIGTSTP comes in while we are
// blocked at waitpid().
weAreWaitingForForegroundProcessToStop = TRUE;
receivedSigtstp = FALSE;
int resultPid = -1;
while (resultPid == -1)
{
resultPid = waitpid(spawnPid, &childExitMethod, 0);
// If we are blocked here at waitpid() and then receive a
// SIGTSTP, waitpid() will return with -1. However, the foreground
// process hasn't actually stopped. When that happens, we need to
// loop back and waitpid() again until the foreground process
// actually stops.
}
// We should update this global variable.
weAreWaitingForForegroundProcessToStop = FALSE;
// We deal with it _now_ if a SIGTSTP came in while we were blocked
// at waitpid().
if (receivedSigtstp == TRUE)
{
receivedSigtstp = FALSE;
implementSigtstpLogic();
}
// Now we need to update our state variables to reflect the way that
// the foreground process terminated:
if (WIFEXITED(childExitMethod) != 0)
{
// The process exited by exit(0), exit(1), return 0, etc.
*statusType = EXIT_VALUE;
*statusValue = WEXITSTATUS(childExitMethod);
}
else if (WIFSIGNALED(childExitMethod) != 0)
{
// The process exited because of an uncaught signal.
*statusType = SIGNAL_RECEIVED;
*statusValue = WTERMSIG(childExitMethod);
printf("terminated by signal %d\n", *statusValue);
} else {
perror("A process ended for reasons unknown!");
exit(1);
}
} else {
// We're running the file in the background, so we aren't going to wait
// for it, but we do have to announce that it's in the background:
char backgroundMessage[STATUS_REPORT_MAX_LENGTH];
sprintf(backgroundMessage, "background pid is %d", spawnPid);
outputStringWithANewline(backgroundMessage);
// We also have to add it to our watch list of processes running in the
// background:
remember(listOfProcesses, spawnPid);
// This use of a linked list that involves pointers to pointers almost
// blows my mind. It was easy enough to write the linked list part,
// but then I realized that passing pointers by value, which I did at
// first, wasn't going to let me change what those pointers were
// pointing to, so I had to go back and make it use pointers to
// pointers.
}
for (i = 0; i < arrayElementsUsed; i++)
{
free(commandArgs[i]);
}
return;
}
int main()
{
// The following handful of variables track the program state:
char commandArray[MAX_COMMAND_ARRAY_SIZE][MAX_STRING_LENGTH];
int arrayElementsUsed = 0;
int statusType = EXIT_VALUE;
int statusValue = 0;
struct runningProcess* listOfProcesses = NULL;
// Make shell ignore SIGINT:
struct sigaction ignoreAction = {{0}};
struct sigaction originalSigintAction = {{0}};
// https://stackoverflow.com/questions/13746033/how-to-repair-warning-missing-braces-around-initializer
ignoreAction.sa_handler = SIG_IGN;
sigaction(SIGINT, &ignoreAction, &originalSigintAction);
// Make shell handle SIGTSTP:
struct sigaction handleSigtstp = {{0}};
handleSigtstp.sa_handler = dealWithSigtstp;
sigfillset(&handleSigtstp.sa_mask);
handleSigtstp.sa_flags = 0; // I don't think this line is necessary.
sigaction(SIGTSTP, &handleSigtstp, NULL);
// The following is the program's main loop:
while (TRUE)
{
checkForFinishedBackgroundProcesses(&listOfProcesses);
// We have to send the _address_ of listOfProcesses, not the value
// of the pointer, because we need to be able to change what it's
// pointing to in the functions that we're now calling. This almost
// blows my mind.
getCommandArray(commandArray, &arrayElementsUsed);
replaceDoubleDollarSigns(commandArray, arrayElementsUsed);
// Now we can check to see if we need to invoke one of the three
// built-in commands:
if (strcmp(commandArray[0], EXIT_COMMAND) == 0)
{
prepForExit(&listOfProcesses);
break;
}
else if (strcmp(commandArray[0], STATUS_COMMAND) == 0)
{
outputStatus(statusType, statusValue);
}
else if (strcmp(commandArray[0], CD_COMMAND) == 0)
{
if (arrayElementsUsed == 1)
{
changeDirectory("");
}
else
{
changeDirectory(commandArray[1]);
}
}
// Or if we're doing nothing:
else if (arrayElementsUsed == 0)
{
// Do nothing; it's a blank line.
}
else if (commandArray[0][0] == COMMENT_SYMBOL)
{
// Do nothing; it's a comment line.
}
// And if none of the above is true, then we need to try to execute
// this command by forking and executing:
else
{
executeCommand
(
commandArray,
arrayElementsUsed,
&statusType,
&statusValue,
&usingBackgroundIsPossible,
&listOfProcesses,
// We have to send the _address_ of listOfProcesses, not the
// value of the pointer, because we need to be able to change
// what it's pointing to in the functions that we're now
// calling. This almost blows my mind.
&originalSigintAction
);
}
}
return 0;
}