CMPS 012B Lab 2 • Unix, shells, gmake solution




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In this lab, you will become familiar with some features of Unix and its shells. Unix interaction is
generally done with either the bash shell or the tcsh shell.
1. Reading assignment
Following are suggested readings to become familiar with Unix :
(a) Your Unix, by Sumitabha Das, chapters 1–4 and 7. If you have a different Unix book, read the
introductory chapters.
(b) Unix is a Four Letter Word… and Vi is a Two Letter Abbreviation, available at :,
is another source for learning Unix.
(d) You should also learn one of the editors vim or emacs. To learn about vim, use the command vimtutor, which will take you through a tutorial. For emacs, type the command emacs & then click
on Help→Emacs Tutorial. The non-GUI form of emacs can be started with emacs -nw.
(e) The UCSC library has subscribed to Safai Books Online
so if you go to that URL using a UCSC computer, you can read them for free. Search for
‘‘Learning the Unix Operating System’’.
2. Symbolic links
In order to make references to my directory easier, you might want to establish symbolic links from
your directories into mine. For example, the command
ln -s /afs/ ~/12b
will create a symbolic link so that you can refer to anything in the course volume using the name
~/12b instead of the whole path.
You could also cd into your lab2 directory and make a symbolic link (symlink) to point at my lab2
directory by using cd to get to your lab2 directory. Then type the command
ln -s ~/12b/Labs-cmps012m/lab2u-unix-shells/ lab2
which will allow you to refer to my lab2 files using the short name lab2. Example : One of the commands below could then be replaced by
grep ’^ *Submit:’ lab2/*.tt
3. Lab exercises
Following are the lab exercises you are to do. For each one submit a file as specified under each
(1) In your working directory for lab2, you made a symbolic link above pointing at mine. Type the
following two commands :
ls -la lab2 >
stat lab2 >>
This will put the output of two commands into a file called, which should show
your symbolic link pointing at my directory.
Submit :
(2) The find(1) command is a useful one for locating files when you know the name or part of it and
don’t remember which directory it is in. Find all of the files in the course volume that contain
the word ‘‘lib’’ as part of the filename :
CMPS-012M • Fall 2013 • Lab 2 • Unix, shells, gmake page 2 of 3
cd /afs/
find . -name ’*lib*’
Note that many error messages are generated to stderr because you don’t have permission to
access some of my directories. Stop this by redirecting stderr :
find . -name ’*lib*’ 2>/dev/null
The file /dev/null is a pseudo-device which discards bytes written to it.1 The above command
works only with bash. Now redirect the output into the file you are to submit :
find . -name ’*lib*’ >~/files.found 2>/dev/null
Submit : files.found
(3) Another useful command, this time for searching files for a given string, is grep(1). Run the
grep ’^ *Submit:’ *.tt
in this lab directory and redirect its output into a file called grep.submit in your directory.
Submit : grep.submit
(4) These commands can be combined using a pipe and xargs(1). Use a command to find all files
anywhere in the course volume
that match the wildcard *.java and pipe this into the command
xargs grep -li lib
The pipe is the stick character (|). Redirect stdout into a file called java.libs.
Submit : java.libs
(5) Write a program in Java that will print the message ‘‘EXIT 1’’ to the standard error and then
exit with a status of 1.
Submit :
(6) Write a shell script called mkexit1 which compiles that program and puts it in a jar file. The
first line of the script must be
#!/bin/sh -x
The second line should be an RCS Id string :
# $Id$
The third line should be your name and username, along with those of your partner, if any.
Also put the RCS Id string in your java program from the previous part. Type the following
commands at a terminal and note that they build a jar :
echo Main-class: exit1 >Manifest
jar cvfm exit1 Manifest exit1.class
yes | rm -i Manifest exit1.class
chmod +x exit1
Put all of them in the script file mkexit1 Use chmod +x mkexit1 to make it executable. Run the
script by typing its name at the command line :
exit1 >/dev/null
echo $?
Note that you still see the error message. The last of these command shows you the exit status.
Submit : mkexit1
(7) Verify that your private directory is properly protected. Use either of the commands
fs la $HOME/private,
fs la ~/private,
and redirect its output into a file called privacy. Append to this file the output from the command echo $HOME.
1. It’s the bit bucket. Empty it when full. 🙂
CMPS-012M • Fall 2013 • Lab 2 • Unix, shells, gmake page 3 of 3
Submit : privacy
(8) Make a copy of, calling it, and have it return an exit status of 255.
Also change the message that it prints to ‘‘EXIT 255’’. Create a Makefile with a target all,
which depends on the jar file exit255. The jar target exit255 depends on exit255.class, which,
in turn, depends on Add commands under the last two dependencies such that it
builds the jar.
Submit :
(9) To this same Makefile, add a target called test, which runs the jar exit255, redirecting its output into a file called 255.output. It then appends the value of the exit status to that same file.
Do not submit 255.output, the grader will create it via gmake test.
Since the exit status is in the shell variable $?, to code that in a Makefile, you need to enter it as
$$?. Also, each line of a Makefile is run as a separate process, so the line that echos the exit
status must be on the same line as the program that is being run, separated by a semi-colon.
Submit : Makefile
(10) Check your quota and find all files larger than 1000 blocks in your file space. The command fs
lq ~ will tell you about your disk quota. The command find ~ -size +1000 will print the
names of all your files larger than 1000 blocks. Redirect the output of both of these commands
into a file called quota.size.
Submit : quota.size
4. What to submit
You were instructed to submit many files. Verify each of them by looking in the submit directory. If
you are in doubt as to the contents of a file you submitted, submit it again. You may submit any file
as many times as you want, as long as you do it before the due date.
If you are doing pair programming, also submit README and PARTNER. Run partnercheck to verify that
your PARTNER file is correct.
Look in the subdirectory .score for instructions to the graders.
Read the submit checklist file in the generic syllabus directory.
2. With apologies to Marcus Porcius Cato Maior (DXX–DCV AUC) : ‹ Praeterea, censeo Microflaccidem esse delendam. ›