added the code filesmain

3 files changed, 170 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..120ce9d
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,5 @@
+./shell: shell.c
+	gcc shell.c -o ./shell
+
+clean:
+	rm -f ./shell
diff --git a/shell.c b/shell.c
new file mode 100644
index 0000000..2d0653d
--- /dev/null
+++ b/shell.c
@@ -0,0 +1,157 @@
+#include <sys/wait.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <limits.h>
+#include <stdbool.h>
+#include "shell.h"
+
+#define MAX_CMD 1024
+#define MAX_PATH 512
+
+int main(int argc, char* argv[]) {
+    // setup an array of the values in $PATH
+    char* pathstr = getenv("PATH");
+    const char* delim = ":";
+    const char* cmddelim = " ";
+    const int binlen = strcnt(pathstr, delim[0]) + 1;
+    char* bins[binlen];
+    char* path = strtok(pathstr, delim);
+    int i = 0;
+    while (path != NULL) {
+        bins[i++] = path;
+        path = strtok(NULL, delim);
+    }
+
+    while (true) {
+        //prefix command, show user, host, cwd
+        char hostbfr[256];
+        gethostname(hostbfr, sizeof(hostbfr));
+        char cwdbfr[MAX_PATH];
+        getcwd(cwdbfr, sizeof(cwdbfr));
+        printf(
+            "[\033[1;32m%s\033[0m@\033[1;31m%s\033[0m]:\033[1;34m%s\033[1;31m$ \033[0m", getenv("USER"), 
+            hostbfr, cwdbfr
+        );
+
+        // get the input string - keep accepting words until a newline
+        char cmdstr[MAX_CMD];
+        scanf("%[^\n]", cmdstr);
+        int c;
+        while ((c = getchar()) != '\n' && c != EOF);    //clear buffer
+
+        // parse the input string into an array, splitting by spaces
+        uint cmdlen = strcnt(cmdstr, cmddelim[0]) + 1;
+        char* cmdarr[cmdlen + 1];
+        char* arg = strtok(cmdstr, cmddelim);
+        i = 0;
+        while (arg != NULL) {
+            cmdarr[i++] = arg;
+            arg = strtok(NULL, cmddelim);
+        }
+
+        //work out if we need to change the cwd
+        if (strcmp(cmdarr[0], "cd") == 0) {
+            // printf("Change directory to '%s'\n", cmdarr[1]);
+            if (chdir(cmdarr[1]) != 0) {
+                printf("\033[0;31mERROR - Could not change cwd\n\033[0m");
+            }
+            continue;
+        }
+
+        //work out if we need to exit
+        if (exitPrefix(cmdstr)) {
+            printf("Exited.\n");
+            break;
+        }
+
+        // try to find a binary
+        strcpy(cmdstr, cmdarr[0]);
+        bool binExists = false;
+        char cmdpath[512];
+        for (i = 0; i < binlen + 1; i++) {
+            if (i >= binlen) {
+                strcpy(cmdpath, cwdbfr);
+            } else {
+                strcpy(cmdpath, bins[i]);
+            }
+            strcat(cmdpath, "/");
+            strcat(cmdpath, cmdstr);
+            if (access(cmdpath, F_OK) != -1) {
+                binExists = true;
+                break;
+            }
+        }
+        if (!(binExists)) {
+            printf("Couldn't find binary - Looked in the following places:\n - %s\n", cwdbfr);
+            for (i = 0; i < binlen; i++) {
+                printf(" - %s\n", bins[i]);
+            }
+            continue;
+        }
+        // printf("Found binary at '%s'\n", cmdpath);
+        cmdarr[cmdlen] = NULL;
+        
+        pid_t pid = fork();
+        bool success = true;
+
+        if (pid == 0) {
+            // printf("Child Process: PID = %i, PPID = %i\n", getpid(), getppid());
+            if (execvp(cmdpath, cmdarr) < 0) {
+                perror("\033[0;31mexec error ");
+                printf("\033[0m");
+                success = false;
+            }
+            break;
+
+        } else {
+            // printf("Parent Process: PID = %i, PPID = %i\n", getpid(), getppid());
+            int status;
+            if (waitpid(pid, &status, 0) < 0) {
+                perror("\033[0;31mwaitpid error ");
+                printf("\033[0m");
+                success = false;
+            }
+            if (success) {
+                printStatus(status);
+            }
+        }
+    }
+    return EXIT_SUCCESS;
+}
+
+// prints out the status code of an exited process.
+// prints in green if the status code is zero. anything
+// else is red.
+void printStatus(int status) {
+    if (status == 0) {
+        printf("\033[0;32m");
+    } else {
+        printf("\033[0;31m");
+    }
+    printf("[Process exited with status code %i]\n\033[0m", status);
+}
+
+// returns an integer of how many times a char was found in a char
+// array
+int strcnt(char* str, const char cnt) {
+    int count = 0;
+    for (int i = 0; i < INT_MAX; i++) {
+        char c = str[i];
+        if (c == '\0') {
+            break;
+        }
+        if (c == cnt) {
+            count++;
+        }
+    }
+    return count;
+}
+
+// returns a boolean if a char array starts with the string "exit"
+bool exitPrefix(const char* cmdstr) {
+    char fourChars[5];
+    strncpy(fourChars, cmdstr, 4);
+    return strcmp(fourChars, "exit") == 0;
+}
\ No newline at end of file
diff --git a/shell.h b/shell.h
new file mode 100644
index 0000000..afbb63b
--- /dev/null
+++ b/shell.h
@@ -0,0 +1,8 @@
+#ifndef SHELL_H
+#define SHELL_H
+
+void printStatus(int status);
+int strcnt(char* str, const char cnt);
+bool exitPrefix(const char* cmdstr);
+
+#endif
\ No newline at end of file