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POIO redirection and buffer issues, fflush and c
 

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  1. POIO redirection and buffer issues, fflush and c
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    <p>for my class we are to implement a shell with output redirection. I have the output redirection working, except my first command is always corrupted see: </p> <pre><code>$ echo this doesn't work H&lt;@?4echo No such file or directory $ echo this does work this does work </code></pre> <p>but every command afterwards seems fine. What technique do I use to find the bug that is causing this problem? </p> <p>I think it has something to do with not fflushing properly. I sprinkled it around my code (which was stupid) to see if it would help during the loop but it did not. I've also tried printing out my OrderedIds list which is just a list of commands to check if I could find H&lt;@?4 anywhere, but even when I initialized it, it did not work. </p> <p>Thanks for your help. </p> <pre><code>#define LENGTH 1000 #define MAXCMD 11 #define MAX_STR_LEN 20 void init(char *temp); void clean(char **orderedIds); void init_pid(int *temp); void reap(int *temp,int ret_status); void jobs(int *pid_list, char **orderedIds); int ioRedir(char **orderedIds); void reap(int *temp,int ret_status){//chainsaws all zombies int a; for (a=0; a&lt;LENGTH; a++ ){ waitpid(temp[a],&amp;ret_status,WNOHANG) == temp[a]; } } void init(char *temp){//Function to initialize/reset the cmd array int i; for(i=0; i&lt;LENGTH; i++){ temp[i] = 0; } } void init_pid(int *temp){//Function to initialize/reset the pid list int i; for(i=0; i&lt;LENGTH; i++){ temp[i] = -777; } } void clean(char **orderedIds){//garbage collection int i; for(i=0; i&lt;MAXCMD; i++){ free(orderedIds[i]); } free(orderedIds); } void jobs(int *pid_list, char **orderedIds){//function to check for background proccesses printf("Jobs:\n"); int y; for(y=0; y&lt;LENGTH; y++){ if(kill(pid_list[y], 0) == 0){ printf("%d\n", pid_list[y]); } } clean(orderedIds); printf("$ "); } int ioRedir(char **orderedIds){ int i; for ( i = 0; i&lt;MAXCMD; i++){ if(orderedIds[i] == NULL){ return -1; } if(strcmp(orderedIds[i],"&gt;")==0){ return (i+1); } } } int main (int argc, char *argv[], char *envp[]) { char temp[LENGTH]; char * tok; char c = '\0'; int saved_stdout; int pid_list[LENGTH]; int ret_status; int numFile; int pid_counter = 0; int outputfd = -1; char outputFile[MAX_STR_LEN]; pid_t pid; printf("$ "); int i, j, y, background= 0; init_pid(pid_list); while(c !=EOF) { //while not ^D // Source: LinuxGazzette Ramankutty outputfd = -1; fflush(0); c = getchar(); if(c=='\n'){ //entered command reap(pid_list, ret_status); char **orderedIds = malloc(MAXCMD * sizeof(char*)); for (i=0; i&lt;MAXCMD; i++){ orderedIds[i] = malloc(MAXCMD * sizeof(char*)); } int k=0; tok = strtok(temp, " \n\t\r"); while (tok !=NULL){ strcpy(orderedIds[k], tok); k++; tok = strtok (NULL, " \n\t\r"); } orderedIds[k] = NULL; //END with NULL init(temp); //initialize the array if(orderedIds[0] ==NULL){ printf("\n$ "); continue; } numFile = ioRedir(orderedIds); if(strcmp(orderedIds[0],"exit")==0){// if exit printf("now exiting...\n"); break; } if(strcmp(orderedIds[k-1], "&amp;")==0){//if background orderedIds[k-1] = NULL; background = 1; }else background = 0; if(strcmp(orderedIds[0], "jobs") == 0){//if jobs command jobs(pid_list, orderedIds); continue; } if(strcmp(orderedIds[0], "cd") == 0){ //if change directory command chdir(orderedIds[1]); printf("$ "); continue; } pid = fork(); if (pid!=0 &amp;&amp; background == 1) { //go to end of list in pid and put it in pid_list[pid_counter] = pid; pid_counter++; printf("To the background: %d\n", pid); } else if (pid==0 &amp;&amp; background == 1) { fclose(stdin); //close child's stdin fopen("/dev/null", "r"); //open a new stdin that is always empty. if(execvp(orderedIds[0], orderedIds)){ printf("%s\n", orderedIds[0]); puts(strerror(errno)); exit(127); } } if (pid != 0 &amp;&amp; !background){ //printf("Waiting for child (%d)\n", pid); fflush(0); pid = wait(&amp;ret_status); } else if (pid == 0 &amp;&amp; !background) { if(numFile &gt; 0){ strncpy(outputFile, orderedIds[numFile], strlen(orderedIds[numFile])); numFile = 0; //open the output file outputfd = open(outputFile, O_WRONLY | O_CREAT | O_TRUNC, S_IRWXU | S_IRGRP | S_IROTH); if (outputfd &lt; 0) { exit(EXIT_FAILURE); } //close STDOUT if(close(STDOUT_FILENO) &lt; 0 ){ perror("close(2) file: STDOUT_FILENO"); close(outputfd); exit(EXIT_FAILURE); } //use dup to rerout the output if(saved_stdout = dup(outputfd) != STDOUT_FILENO){ perror("dup(2)"); close(outputfd); exit(EXIT_FAILURE); } close(outputfd); } if (execvp(orderedIds[0], orderedIds)){ printf("%s\n", orderedIds[0]); puts(strerror(errno)); exit(127); } } dup2(saved_stdout,outputfd); clean(orderedIds); fflush(0); printf("$ "); } else { strncat(temp, &amp;c, 1); } } fflush(0); return 0; } </code></pre>
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    1. COYou could save us all a lot of questions by show us (a) an example of a command set that is failing, (b) what it *should* look like on success, and (c) enlighten us with any debugging steps you've taken so far. Entering the words "first command" is not an option. Please provide detailed steps as to what your shell is *supposed* to accept as input, and what its output *should* look like.
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      1. USWhozCraig
    2. COWill do. As I've shown an example of a command set that is failing is "first command" where it should tell me that "first" is no such file or directory, but instead it has some junk in front of it. I will edit the question to show more of what you're asking. As far as debugging goes, It was the only question that I asked: What technique do I use to find the bug? So far I've tried using fflush but it didn't work.
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      1. USHarrison
 

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