Advanced Programming in the UNIX® Environment

ptg10805159

Section 4.3 File Types 97

ptr = "directory";

else if (S_ISCHR(buf.st_mode))

ptr = "character special";

else if (S_ISBLK(buf.st_mode))

ptr = "block special";

else if (S_ISFIFO(buf.st_mode))

ptr = "fifo";

else if (S_ISLNK(buf.st_mode))

ptr = "symbolic link";

else if (S_ISSOCK(buf.st_mode))

ptr = "socket";

else

ptr = "** unknown mode **";

printf("%s\n", ptr);

}

exit(0);

}

Figure 4.3 Print type of file for each command-line argument

Sample output from Figure4.3 is

$./a.out /etc/passwd /etc /dev/log /dev/tty \

>/var/lib/oprofile/opd_pipe /dev/sr0 /dev/cdrom

/etc/passwd: regular

/etc: directory

/dev/log: socket

/dev/tty: character special

/var/lib/oprofile/opd_pipe: fifo

/dev/sr0: block special

/dev/cdrom: symbolic link

(Here, we have explicitly entered a backslash at the end of the first command line,

telling the shell that we want to continue entering the command on another line. The

shell then prompted us with its secondary prompt,>, on the next line.) We have

specifically used thelstatfunction instead of thestatfunction to detect symbolic

links. If we used thestatfunction, we would never see symbolic links.

Historically,early versions of the UNIX System didn’t provide the S_ISxxx

macros. Instead, we had to logically AND thest_modevalue with the maskS_IFMT

and then comparethe result with the constants whose names areS_IFxxx.Most

systems define this mask and the related constants in the file<sys/stat.h>.Ifwe

examine this file, we’ll find theS_ISDIRmacrodefined something like

#define S_ISDIR(mode) (((mode)&S_IFMT) == S_IFDIR)

We’ve said that regular files arepredominant, but it is interesting to see what

percentage of the files on a given system are of each file type. Figure4.4 shows the

counts and percentages for a Linux system that is used as a single-user workstation.

This data was obtained from the program shown in Section 4.22.