Thread: Confusion with new line char - command line shell arguments

You should rename the c parameter to filename as "c" does not describe what the parameter is for.

Since you intend to read line by line, why not use fgets instead?

Originally Posted by laserlight

You should rename the c parameter to filename as "c" does not describe what the parameter is for.

Since you intend to read line by line, why not use fgets instead?

I looked into fgets, and assumed that it was for just one character. I only know how to do strtok on a pointer array. (C is brand new to me).

It's pretty confusing since it's very barebones.

Could you show me how fgets would work?

Thank you!

*edit*
Here's my attempt at that.

Code:

void batchMode(char *c){     
     char *tok[100];     
     char *batchTokens;    
     char *batchBuffer = NULL;     
     size_t batchSize = 0;     

     FILE *fp = fopen(c, "r");

        if (fp != NULL){
       
             while (fgets(batchTokens, sizeof batchTokens, fp) != NULL){
                  int i = 0;

                  char *btok = strtok(batchTokens, "\t\n");
                  while (btoks && i < 99) {
                       tok[i++] = btok;
                       btok = strtok(NULL, " \t\n");
                  }
    
            tok[i] = NULL;
            pid_t bFork = fork();

            if (bFork == (pid_t) -1)
                 perror("fork");

            else if (bFork == 0){
                 execvp(tok[i], tok);

            else {
                 int status;
                 waitpid(bFork, &status, 0);
           }

          }

       }

}

Start with something simple, e.g., reading the file line by line and printing its contents:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int processBatch(const char *filename);

int main(void) {
    const char *filename = "example.sh";
    if (!processBatch(filename)) {
        fprintf(stderr, "Error: could not process batch file '%s'\n", filename);
        return EXIT_FAILURE;
    }
    return 0;
}

int processBatch(const char *filename) {
    FILE *fp = fopen(filename, "r");
    if (!fp) {
        fprintf(stderr, "Error: could not open batch file\n");
        return 0;
    }

    unsigned int line_no = 1;
    char buffer[BUFSIZ];
    while (fgets(buffer, sizeof(buffer), fp)) {
        char *newline = strchr(buffer, '\n');
        if (!newline) {
            fprintf(stderr, "Error: batch file line %u exceeds %zu characters\n", line_no, sizeof(buffer) - 1);
            return 0;
        }

        *newline = '\0'; // remove the trailing newline
        printf("Line %u: %s\n", line_no, buffer);
        ++line_no;
    }

    fclose(fp);
    return 1;
}

You could then either improve this by say, skipping blank lines, or handling a last line that doesn't end in a new line (or perhaps leaving it as an error), or even using dynamic memory allocation to have a variable length buffer (or switching to the non-standard though POSIX standard getline function). When you're satisfied, then you change the printf into the part where you fork and do the execvp call.

Thank you very much. I'll work with it now.

Code:

#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<errno.h>


#define bSize 1000


void driveLoop();
char *userInput(void);
void removeExit(char *original, char *subString); // removes string with substring "exit"
void batchMode(char *c);


int main(int argc, char **argv){




  char *fTemp;
  if (argc == 1)
    driveLoop(); // calls the loop function that accepts input and executes commands.


  else if (argc == 2)
    batchMode(&argv[1][0]);
            
  
  return 0;


}


void driveLoop(void){
  char *comTokens[100];
  char *tempTokens;
  char *command;
  char *cd;
  char *cdDir;
  char* cdTemp;
  char cdBuf[bSize];
  char checkExit[] = "exit";
  
  for (;;){


    printf("> ");
    command = userInput(); // reads input


    if (!*command) // allows for empty string error
      break;


    char *exitPtr = strstr(command, "exit"); // returns a value to a pointer if substring is found
    removeExit(command, "exit"); 
    puts(command); // updates the array after the function filter
    
    int i = 0;
    tempTokens = strtok(command, " \t\n"); // tokens are how the computer recognizes shell commands


    while (tempTokens && i < 99){ // geeksforgeeks.com
      comTokens[i++] = tempTokens;
      tempTokens = strtok(NULL, "\t\n");
    }


    if (strcmp(comTokens[0], "exit") == 0) // exit if input is "exit" only
      exit(0); 




    if(strcmp(comTokens[0], "cd") == 0){ // built in change directory command
      cd = getcwd(cdBuf, sizeof(cdBuf));
      cdDir = strcat(cd, "/");
      cdTemp = strcat(cdDir, comTokens[1]); // cplusplus.com reference
      chdir(cdTemp);
      continue;
    }
    
    comTokens[i] = NULL;


    pid_t cFork = fork(); // creates duplicate child process of parent


    if (cFork == (pid_t) - 1){ // error check
      perror("fork");
    }


    else if (cFork == 0) { // error codes found on cplusplus.com
      execvp(comTokens[0], comTokens);
      perror("exec");      
    }
    
    else { // children are returned. parent executes
      int status;
      waitpid(cFork, &status, 0);
      if (exitPtr != NULL){ // if substring exit was found, exit the program
    exit(0);
      }
    }


  }
  
}


char *userInput(void){  // referenced Linux man page - getline(3) (linux.die.net)
  char *input = NULL;
  size_t size = 0;
  getline(&input, &size, stdin); // updates the size as it goes along
  return input;
}


void removeExit(char *original, char *subString){ // removes exit from string
  char *ex;
  int len = strlen(subString); 
  while ((ex = strstr(original, subString))){ // Referenced from a Stack Overflow page.
    *ex = '\0';
    strcat(original, ex+len);
  }
}


void batchMode(char *c){


  char *tok[100];
  char *batchTokens;
  char *batchBuffer = NULL;
  size_t batchSize = 0;


  FILE *fp = fopen(c, "r");


  unsigned int line = 1;
  char buffer[bSize];


  while(fgets(buffer, sizeof(buffer), fp)){
      
      int i = 0;


      char *toks = strtok(buffer, "\t\n");


      while (toks && i < 99){
           tok[i++] = toks;
           toks = strtok(NULL, " \t\n");
      }


      tok[i] = NULL;
          pid_t bFork = fork();


      if (bFork == (pid_t) - 1)
          perror("fork");


      else if (bFork == 0){
         execvp(tok[i], tok);
         perror("exec");
      }


      else {
        int status;
        waitpid(bFork, &status, 0);
      }
    
  }
  
}

How's my fget?