implementation of the `mkdir` command with `-p` parameter in C

Question

I wrote a program that implements the mkdir command with the -p parameter to create the parent directly if it does not exist.

My question is, is this implementation optimal? What else could I improve or what problems does implementation have?

code:

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <stdbool.h>
#include <limits.h>
#include "lab.h"

bool vFlag = 0;
bool pFlag = 0;

int main(int argc, char* argv[])
{
    bool err = false;
    int option;

    // check for optional arguments
    while((option = getopt(argc,argv,"vp")) !=-1)
        switch(option)
        {
            case 'v':
                vFlag = 1;
                break;

            case 'p':
                pFlag = 1;
                break;
        }
    
    if(argc == 1)
    {
        err_msg("missing operand\nTry 'mkdir --help' for more information.");
        exit(1);
    }
    
    for(int i=optind; i<argc; i++)
    {
        
        if(pFlag)
        {
            char* pStart = argv[optind];
            char* pCurrent = argv[optind];
            char* pLast = strrchr(argv[optind], '/');
            
            while(*pCurrent != '\0')
            {
                if (*pCurrent == '/' || *pCurrent == '.') 
                {
                    char str[20] = {0};
                    strncpy(str, pStart, pCurrent - pStart);
                    
                    if((access(str, X_OK) != 0) && (access(str, F_OK) == 0))
                    {
                        err_msg("cannot create directory '%s': Permission denied", str);
                        exit(1);
                    }
                    else
                    {
                        mkdir(str, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
                        if (chdir(str) < 0)
                        {
                            perror("chdir");
                        }
                    }
                    pStart = pCurrent+1;
                }
                ++pCurrent;
            }
            mkdir(pLast+1, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
            return 0;
        }

        if(access(argv[i],F_OK) == 0)
        {
            err_msg("cannot create directory ‘%s’: File exists",argv[i]);
            err = true;
        }
        else
        {
            if(mkdir(argv[i], S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH) == -1)
            {
                err_ret("cannot create directory '%s'",argv[i]);
                exit(1);
            }
            else
                if (vFlag)
                    printf("mkdir: created directory '%s'\n", argv[i]);
        }
    }
    if(err == false)
        exit(0);
    else
        exit(1);
}

lab.h content:

/* Our own header, to be included *after* all standard system headers */

#ifndef __LAB_H__
#define __LAB_H__

#include    <sys/types.h>   /* required for some of our prototypes */
#include    <stdio.h>       /* for convenience */
#include    <stdlib.h>      /* for convenience */
#include    <string.h>      /* for convenience */
#include    <unistd.h>      /* for convenience */

#define MAXLINE 4096            /* max line length */

#define FILE_MODE   (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
                    /* default file access permissions for new files */
#define DIR_MODE    (FILE_MODE | S_IXUSR | S_IXGRP | S_IXOTH)
                    /* default permissions for new directories */


                    /* prototypes for our own functions */
char    *path_alloc(int *);         /* {Prog pathalloc} */
int      open_max(void);            /* {Prog openmax} */
void     clr_fl(int, int);          /* {Prog setfl} */
void     set_fl(int, int);          /* {Prog setfl} */

void    err_dump(const char *, ...);    /* {App misc_source} */
void    err_msg(const char *, ...);
void    err_quit(const char *, ...);
void    err_ret(const char *, ...);
void    err_sys(const char *, ...);

#endif  /* __LAB_H__ */

I chose 20 to be large enough to store the directory name in the variable. But better modified with PATH_MAX. It's better this way? — Mark
– Mark, Commented Apr 11, 2022 at 16:29
lab.h deserves improvements, yet I assume it it only here as a reference. — chux
– chux, Commented Apr 11, 2022 at 21:40

chux · Accepted Answer · 2022-04-12 11:13:46Z

Just a little feedback.

Documentation

Code deserves at least an overall description of its goal. Consider self documenting by incorporating a help option that details the goal.

        case 'h':
            puts(
              "An implementation of the `mkdir` command with `-p` parameter.\n"
              "-p does this.\n"
              "-v does that.\n"
              "...\n"         
              "Come and listen to my story about a man named Jed ...\n"
              "...\n"         
              "Lorem ipsum dolor sit amet, consectetur adipiscing elit ...\n");

Detect string trouble

OP's code neither efficiently nor robustly handles string formation. Use a buffer to handle the maximum expected path and detect excessive arguments.

    // char str[20] = {0};
    // strncpy(str, pStart, pCurrent - pStart);

    char str[PATH_MAX+0];  // See note below
    int length = snprintf(str, sizeof str, "%s", pStart);
    if (length < 0 || (unsigned) length >= sizeof str) {
      err_ret("Path too long '%.20s...'", pStart);
      exit(1);
    }

PATH_MAX is apparently the maximum size, not string length as from strlen(), so that value includes space for the null character. # chars in a path name including nul.

Sentence vs. lower case messages

Example:

            // err_ret("cannot create directory '%s'",argv[i]);
            err_ret("Cannot create directory '%s'.",argv[i]);
            //       ^                           ^

After exit/return, omit else

if(err == false)
    exit(0);
// else
exit(1);

Or in this case:

exit(!!err);

@Mark What overflow? If it relates to Detect string trouble, how does that not address the issue? — chux
– chux, Commented Apr 12, 2022 at 17:52

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