Description
1. Overview
In this lab you will be introduced to a simple Unix systems programming problem,
namely printing out statistics about files. We present the program in the form of a
Unix man(1) page. You will also need to read man pages as listed.
NAME
l8stat — stat a list of files
SYNOPSIS
l8stat [filename …]
DESCRIPTION
Each argument is a filename whose statistics are to be printed. If no filenames are given, the current directory (.) is used. For each file, print the
mode, the file size in bytes , the file or link modification time, and the name. If
a file is a symbolic link, the value of the link is also printed. If the time is
more than 180 days from the current time, the month, day, and year are
printed, otherwise, the month, day, and time.
EXIT STATUS
0 No errors were detected.
1 Errors were detected and messages printed.
SEE ALSO
ls(1), man(1), stat(1), lstat(2), readlink(2), time(2), localtime(3), strerror(3),
strftime(3).
2. Notes
To prepare for writing this lab, read several man(1) pages which describe the system
calls and library functions you need to use. The number in parentheses indicates
the chapter : (1) User commands, (2) System calls, and (3) C library functions.
(α) The commands ls(1) and stat(1) show information about files. The Perl program l8stat.perl is a reference implementation, and your program should
produce the same output.
(β) Manual pages can be read using the man(1) command. Each man page is in a
particular section, so, for example, the command
man -s 3 printf
can display the man page for printf(3). The number in parentheses indicates
the manual section.
(γ) You may use the x command from /afs/cats.ucsc.edu/courses/cmps012b-wm/
bin (in your path) to displayaman page in a new xterm :
x man -s 3 printf &
CMPS-012M • Fall 2013 • Lab 8 • Unix programming page 2 of 2
(δ) The system call lstat(2) provides information about a file (or a link, if it is a
link). The information is in a struct stat, and you will use the fields st_mode,
st_size, and st_mtime. The mode is printed as 6 octal digits, and the size as 9
decimal digits.
(ε) If lstat fails, print an error message in the standard format and continue.
(ζ) The system call readlink(2) will return information about the symbolic link, if
the file is a symbolic link. If it fails, assume that the file is not a symlink and
ignore the failure.
(η) The system call time(2) returns the current time in seconds since the Epoch
(Thu Jan 1 00:00:00 1970 UTC) as a value of type time_t.
(θ) The C library function localtime(3) accepts a value of type time_t, and using
the local time, formats it into a struct tm suitable for printing.
(ι) The C library function strerror(3) accepts the variable errno and returns a
suitable formatted string indicating a reason for a failed system call.
(κ) The C library function strftime(3) accepts a format string and a struct tm and
returns a string suitable for printing. Use the format string “%b %e %R” if the
time is within 180 days of the current time (whether in the past or in the
future) and “%b %e %Y” if beyond that time. The symbol ‘‘ ’’ isavisible space,
which you should type into your program as an ordinary space.
3. What to submit
Submit README, Makefile, l8stat.c. Your Makefile must build an executable binary
called l8stat. Also, if you are doing pair programming, submit the required pair
programming files.
