Week 08 Laboratory Exercises

Objectives

  • learning how to access file metadata via stat
  • learning how to use file metadata
  • practicing file operations generally
  • understand make's core operation

Preparation

Before the lab you should re-read the relevant lecture slides and their accompanying examples.

Getting Started

Create a new directory for this lab called lab08, change to this directory, and fetch the provided code for this week by running these commands: 

mkdir lab08
cd lab08
1521 fetch lab08

Or, if you're not working on CSE, you can download the provided code as a zip file or a tar file.

Exercise — in pairs:
Print Files Sizes

We are worried about disk usage and would like to know how much space is used used by a set of files

Write a C program, file_sizes.c, which is given one or more filenames as command line arguments. It should print one line for each filename which gives the size in bytes of the file. It should also print a line giving the combined number of bytes in the files.

Follow the output format below.

Do not read the file - obtain the file size from the function stat. 

dcc file_sizes.c -o file_sizes
./file_sizes bubblesort.c print_bigger.c swap_numbers.c unordered.c
bubblesort.c: 667 bytes
print_bigger.c: 461 bytes
swap_numbers.c: 565 bytes
unordered.c: 486 bytes
Total: 2179 bytes
./file_sizes bubblesort.s print_bigger.s swap_numbers.s unordered.s numbers1.txt numbers2.txt sorted.txt
bubblesort.s: 1142 bytes
print_bigger.s: 1140 bytes
swap_numbers.s: 1173 bytes
unordered.s: 791 bytes
numbers1.txt: 59 bytes
numbers2.txt: 55 bytes
sorted.txt: 21 bytes
Total: 4381 bytes

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest file_sizes

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab08_file_sizes file_sizes.c

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
Print File Modes

We would like to print the access permissions for a set of files

Write a C program, file_modes.c, which is given one or more pathnames as command line arguments. It should print one line for each pathnames which gives the permissions of the file or directory.

Follow the output format below.

dcc file_modes.c -o file_modes
ls -ld file_modes.c file_modes file_sizes.c file_sizes
-rwxr-xr-x 1 z5555555 z5555555 116744 Nov  2 13:00 file_sizes
-rw-r--r-- 1 z5555555 z5555555    604 Nov  2 12:58 file_sizes.c
-rwxr-xr-x 1 z5555555 z5555555 222672 Nov  2 13:00 file_modes
-rw-r--r-- 1 z5555555 z5555555   2934 Nov  2 12:59 file_modes.c
./file_modes file_modes file_modes.c file_sizes file_sizes.c
-rwxr-xr-x file_modes
-rw-r--r-- file_modes.c
-rwxr-xr-x file_sizes
-rw-r--r-- file_sizes.c
chmod 700 file_modes
chmod 640 file_sizes.c
chmod 600 file_modes.c
ls -ld file_modes.c file_modes file_sizes.c file_sizes
-rwxr-xr-x 1 z5555555 z5555555 116744 Nov  2 13:00 file_sizes
-rw-r----- 1 z5555555 z5555555    604 Nov  2 12:58 file_sizes.c
-rwx------ 1 z5555555 z5555555 222672 Nov  2 13:00 file_modes
-rw------- 1 z5555555 z5555555   2934 Nov  2 12:59 file_modes.c
./file_modes file_modes file_modes.c file_sizes file_sizes.c
-rwx------ file_modes
-rw------- file_modes.c
-rwxr-xr-x file_sizes
-rw-r----- file_sizes.c
The first character on each line should be '-' for ordinary files and 'd' for directories. For example: 
./file_modes /tmp /web/cs1521/index.html
drwxrwxrwx /tmp
-rw-r--r-- /web/cs1521/index.html

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest file_modes

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab08_file_modes file_modes.c

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Exercise — in pairs:
Compile C Files If Needed

You have been given compile_if_needed.c, a C program that given the pathname of single file C programs compiles them. For example: 
dcc compile_if_needed.c -o compile_if_needed
./compile_if_needed file_sizes.c file_modes.c
/usr/local/bin/dcc file_modes.c -o file_modes
/usr/local/bin/dcc file_sizes.c -o file_sizes
Unfortunately the code you have been given is inefficient. It recompiles the C file even if this is not necessary.

Modify compile_if_needed.c so that it only compiles C files if necessary.

A compilation is necessary if the binary doesn't exist.

A compilation is also necessary if the C file has been changed since the last compilation. In other words, if the modification time of the C file is more recent than the binary.

Follow the output format below.

./compile_if_needed file_sizes.c file_modes.c
/usr/local/bin/dcc file_modes.c -o file_modes
/usr/local/bin/dcc file_sizes.c -o file_sizes
./compile_if_needed file_sizes.c file_modes.c
file_modes.c does not need compiling
file_sizes.c does not need compiling
rm file_sizes
./compile_if_needed file_sizes.c file_modes.c
file_modes.c does not need compiling
/usr/local/bin/dcc file_sizes.c -o file_sizes
echo >> file_sizes.c # add a new-line to file_sizes.c
./compile_if_needed file_sizes.c file_modes.c
file_modes.c does not need compiling
/usr/local/bin/dcc file_sizes.c -o file_sizes
./compile_if_needed file_sizes.c file_modes.c
file_modes.c does not need compiling
file_sizes.c does not need compiling
./compile_if_needed file_sizes.c file_modes.c
file_modes.c does not need compiling
file_sizes.c does not need compiling

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest compile_if_needed

When you are finished working on this exercise, you and your lab partner must both submit your work by running give: 

give cs1521 lab08_compile_if_needed compile_if_needed.c

Note, even though this is a pair exercise, you both must run give from your own account before Wednesday 01 January 00:00 to obtain the marks for this lab exercise.

Challenge Exercise — individual:
ls -ld

We need clean room implementation of the standard Unix program ls.

Write a C program, lsld.c, which is given zero or more pathnames as command line arguments produces exactly the same output as ls -ld given the same pathnames as arguments.

Except ls -ld sorts its output lines. You do not have to match this.

Follow the output format below.

dcc lsld.c -o lsld
ls -ld lsld.c lsld file_sizes.c file_sizes /home/cs1521/public_html
drwxr-xr-x 6 cs1511   cs1511      128 Sep 16 08:02 /home/cs1521/public_html
-rwxr-xr-x 1 z5555555 z5555555 116744 Nov  2 13:00 file_sizes
-rw-r--r-- 1 z5555555 z5555555    604 Nov  2 12:58 file_sizes.c
-rwxr-xr-x 1 z5555555 z5555555 222672 Nov  2 13:00 lsld
-rw-r--r-- 1 z5555555 z5555555   2934 Nov  2 12:59 lsld.c
./lsld lsld.c lsld file_sizes.c file_sizes /home/cs1521/public_html
-rw-r--r-- 1 z5555555 z5555555   2934 Nov  2 12:59 lsld.c
-rwxr-xr-x 1 z5555555 z5555555 222672 Nov  2 13:00 lsld
-rw-r--r-- 1 z5555555 z5555555    604 Nov  2 12:58 file_sizes.c
-rwxr-xr-x 1 z5555555 z5555555 116744 Nov  2 13:00 file_sizes
drwxr-xr-x 6 cs1511   cs1511      128 Sep 16 08:02 /home/cs1521/public_html

When you think your program is working, you can use autotest to run some simple automated tests: 

1521 autotest lsld

When you are finished working on this exercise, you must submit your work by running give: 

give cs1521 lab08_lsld lsld.c

You must run give before Wednesday 01 January 00:00 to obtain the marks for this lab exercise. Note that this is an individual exercise, the work you submit with give must be entirely your own.

Submission

When you are finished each exercises make sure you submit your work by running give.

You can run give multiple times. Only your last submission will be marked.

Don't submit any exercises you haven't attempted.

If you are working at home, you may find it more convenient to upload your work via give's web interface.

Remember you have until Wednesday 01 January 00:00 to submit your work.

You cannot obtain marks by e-mailing your code to tutors or lecturers.

You check the files you have submitted here.

Automarking will be run by the lecturer several days after the submission deadline, using test cases different to those autotest runs for you. (Hint: do your own testing as well as runningautotest.)

After automarking is run by the lecturer you can view your results here. The resulting mark will also be available via give's web interface.

Lab Marks

When all components of a lab are automarked you should be able to view the the marks via give's web interface or by running this command on a CSE machine: 

1521 classrun -sturec