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円')
 {
 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__ */

• chux: Why 20 in char str[20]?
• Mark: what is wrong with 20?
• Mark: 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?
• chux: lab.h deserves improvements, yet I assume it it only here as a reference.

Answer 1

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);

• chux: @Mark What overflow? If it relates to Detect string trouble, how does that not address the issue?