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I am trying to write a small C program that emulates the unix command
ls -l. To do so, I am using the stat(2) syscall and have ran into a small hiccup writing the permissions. I have a mode_t variable which holds the file permissions from st_mode, and it wouldn't be hard to parse that value into s string representation, but I was just wondering if there is a better way to be doing it than that.
501
The stat() function gets status information about a specified file and places it in the area of memory pointed to by the buf argument. If the named file is a symbolic link, stat() resolves the symbolic link. It also returns information about the resulting file.
To view the permissions for all files in a directory, use the ls command with the -la options. Add other options as desired; for help, see List the files in a directory in Unix. In the output example above, the first character in each line indicates whether the listed object is a file or a directory.
Permissions of 644 mean that the owner of the file has read and write access, while the group members and other users on the system only have read access. For executable files, the equivalent settings would be 700 and 755 which correspond to 600 and 644 except with execution permission.
755 means read and execute access for everyone and also write access for the owner of the file. When you perform chmod 755 filename command you allow everyone to read and execute the file, the owner is allowed to write to the file as well.
example from google
#include <unistd.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
int main(int argc, char **argv)
{
if(argc != 2)
return 1;
struct stat fileStat;
if(stat(argv[1], &fileStat) < 0)
return 1;
printf("Information for %s\n", argv[1]);
printf("---------------------------\n");
printf("File Size: \t\t%d bytes\n", fileStat.st_size);
printf("Number of Links: \t%d\n", fileStat.st_nlink);
printf("File inode: \t\t%d\n", fileStat.st_ino);
printf("File Permissions: \t");
printf( (S_ISDIR(fileStat.st_mode)) ? "d" : "-");
printf( (fileStat.st_mode & S_IRUSR) ? "r" : "-");
printf( (fileStat.st_mode & S_IWUSR) ? "w" : "-");
printf( (fileStat.st_mode & S_IXUSR) ? "x" : "-");
printf( (fileStat.st_mode & S_IRGRP) ? "r" : "-");
printf( (fileStat.st_mode & S_IWGRP) ? "w" : "-");
printf( (fileStat.st_mode & S_IXGRP) ? "x" : "-");
printf( (fileStat.st_mode & S_IROTH) ? "r" : "-");
printf( (fileStat.st_mode & S_IWOTH) ? "w" : "-");
printf( (fileStat.st_mode & S_IXOTH) ? "x" : "-");
printf("\n\n");
printf("The file %s a symbolic link\n", (S_ISLNK(fileStat.st_mode)) ? "is" : "is not");
return 0;
}
result:
Information for 2.c --------------------------- File Size: 1223 bytes Number of Links: 1 File inode: 39977236 File Permissions: -rw-r--r-- The file is not a symbolic link
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