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Program 1 – CS 344

This assignment asks you to write bash shell scripts to compute matrix operations. The purpose is to get you

familiar with the Unix shell, shell programming, Unix utilities, standard input, output, and error, pipelines,

process ids, exit values, and signals (at a basic level).

What you’re going to submit is your script, called simply “matrix”.

Overview

In this assignment, you will write a bash shell script that calculates basic matrix operations using input from

either a file or stdin. The input will be whole number values separated by tabs into a rectangular matrix. Your

script should be able to print the dimensions of a matrix, transpose a matrix, calculate the mean vector of a

matrix, add two matrices, and multiply two matrices.

You will be using bash builtins and Unix utilities to complete the assignment. Some commands to read up on

are while , cat , read , expr , cut , head , tail , wc , and sort .

Your script must be called simply “matrix”. The general format of the matrix command is:

matrix OPERATION [ARGUMENT]…

Refer to man(1) (You can do this with the command `man 1 man`) for an explanation of the conventional

notation regarding command syntax, to understand the line above. Note that many terminals render italic

font style as an underline:

matrix OPERATION [ARGUMENT]…

Specificaons

Your program must perform the following operations: dims, transpose, mean, add, and multiply. Usage is as

follows:

matrix dims [MATRIX]

matrix transpose [MATRIX]

matrix mean [MATRIX]

matrix add MATRIX_LEFT MATRIX_RIGHT

matrix multiply MATRIX_LEFT MATRIX_RIGHT

The dims, transpose, and mean operations should either perform their respective operations on the file

named MATRIX, or on a matrix provided via stdin. The add and multiply operations do not need to process

input via stdin.

dims should print the dimensions of the matrix as the number of rows, followed by a space, then the

number of columns.

transpose should reflect the elements of the matrix along the main diagonal. Thus, an MxN matrix will

become an NxM matrix and the values along the main diagonal will remain unchanged.

mean should take an MxN matrix and return an 1xN row vector, where the first element is the mean of

column one, the second element is the mean of column two, and so on.

add should take two MxN matrices and add them together element-wise to produce an MxN matrix. add

should return an error if the matrices do not have the same dimensions.

multiply should take an MxN and NxP matrix and produce an MxP matrix. Note that, unlike addition,

matrix multiplication is not commutative. That is A*B != B*A.

Here is a brief example of what the output should look like.

$ cat m1

1 2 3 4

5 6 7 8

$ cat m2

1 2

3 4

5 6

7 8

$ ./matrix dims m1

2 4

$ cat m2 | ./matrix dims

4 2

$ ./matrix add m1 m1

2 4 6 8

10 12 14 16

$ ./matrix add m2 m2

2 4

6 8

10 12

14 16

$ ./matrix mean m1

3 4 5 6

$ ./matrix transpose m1

1 5

2 6

3 7

4 8

$ ./matrix multiply m1 m2

50 60

114 140

You must check for the right number and format of arguments to matrix. This means that, for example, you

must check that a given input file is readable, before attempting to read it. You are not required to test if the

input file itself is valid. In other words, the behavior of matrix is undefined when the matrix input is not a valid

matrix. for the purposes of this assignment, a valid matrix is a tab-delimited table containing at least one

element, where each element is a signed integer, every entry is defined, and the table is rectangular.

The following are examples of invalid matrices. Our grading script (see below) does not send these as input

into your matrix program. Similarly, you aren’t allowed to send matrices with these characteristics as output

from your script either, and we will test your output to make sure it doesn’t. If any of these are found in your

output, the grading script will deduct points:

An empty matrix.

A matrix where the final entry on a row is followed by a tab character.

A matrix with empty lines.

A matrix with any element that is blank or not an integer.

Here is a valid matrix file, m1:

$ cat m1

8 5 6

3 2 2

1 6 7

5 0 7

2 2 4

$ cat -A m1 # The ‘-A’ flag shows tabs as ‘^I’ and newlines as ‘$’. This is a good way to check correctness.

8^I5^I6$

3^I2^I2$

1^I6^I7$

5^I0^I7$

2^I2^I4$

$

If the inputs are valid — your program should output only to stdout, and nothing to stderr. The return value

should be 0.

If the inputs are invalid — your program should output only to stderr, and nothing to stdout. The return value

should be any number except 0. The error message you print is up to you; you will receive points as long as

you print something to stderr and return a non-zero value.

Your program will be tested with matrices up to dimension 100 x 100.

Though optional, I do recommend that you use temporary files; arrays are not recommended. For this

assignment, anytemporary files you use should be put in the current working directory. (A more standard

place for temporary files is in /tmp but don’t do that for this assignment; it makes grading easier if they are in

the current directory.) Be sure any temporary file you create uses the process id as part of its name, so that

there will not be conflicts if the program is running more than once. Be sure you remove any temporary files

when your program is done. You should also use the trap command to catch interrupt, hangup, and

terminate signals to remove the temporary files if the program is terminated unexpectedly.

All values and results are and must be integers. You may use the expr command to do your calculations, or

any other bash shell scripting method, such as ((expr)) . Do not use any other languages other than bash

shell scripting: this means that, among others, awk, sed, tcl, bc, perl, & the python languages and tools

are off-limits for this assignment. Note that expr only works with whole numbers. When you calculate the

average you must round to the nearest integer, where half values round away from 0 (i.e. 7.5 rounds up to 8,

but -7.5 rounds down to -8). This is the most common form of rounding. When doing truncating integer

division (as bash does), this formula works to divide two numbers and end up with the proper rounding:

(a + (b/2)*( (a>0)*2-1 )) / b

You can learn more about rounding methods here:

Rounding – Wikipedia (https://en.wikipedia.org/wiki/Rounding#Round_half_away_from_zero)

Grading With a Script

To make it easy to see how you’re doing, you can download the actual grading script here:

p1gradingscript

To use the script, just place it in the same directory as your matrix script and run it like this:

$ ./p1gradingscript matrix

Be aware that this script might take a minute or two to run, depending on how speedy your algorithms and

code are, since there’s a lot of matrix math in there. The grading script has generous time-outs for each test

— if your script takes too long to complete a command, the test will time out and you will receive 0 points for

that particular test. If you have any doubt about your running time being acceptable, just add a note into your

code as a comment at the top to warn the TA. When we run your script for grading, we will do this to put

your results into a file we can examine more easily:

$ ./p1gradingscript matrix > grading_result.username

To compare yours to a perfect solution, you can download here a completely correct run of the script that

shows what you should get if everything is working correctly:

p1perfectoutput

The p1gradingscript itself is a good resource for seeing how some of the more complex shell scripting

commands work, too.

Summary

Your script must support the following operations:

matrix dims [MATRIX]

Prints error message to stderr, nothing to stdout and return value != 0 if:

Argument count is greater than 1 (e.g. `matrix dims m1 m2`).

Argument count is 1 but the file named by argument 1 is not readable (e.g. `matrix dims no_such_file`).

Otherwise, prints “ROWS COLS” (Space separated!) to stdout, nothing to stderr, and returns 0.

matrix transpose [MATRIX]

Prints error message to stderr, nothing to stdout and return value != 0 if:

Argument count is greater than 1 (e.g. `matrix transpose m1 m2`).

Argument count is 1 but the file named by argument 1 is not readable (e.g. `matrix transpose

no_such_file`).

Otherwise, prints the transpose of the input, in a valid matrix format to stdout, nothing to stderr, and

returns 0.

matrix mean [MATRIX]

Prints error message to stderr, nothing to stdout and return value != 0 if:

Argument count is greater than 1 (e.g. `matrix mean m1 m2`).

Argument count is 1 but the file named by argument 1 is not readable (e.g. `matrix mean no_such_file`).

Otherwise, prints a row vector mean of the input matrix, in a valid matrix format to stdout, nothing to

stderr, and returns 0. All values must round to the nearest integer, with ***.5 values rounded away from

zero.

matrix add MATRIX_LEFT MATRIX_RIGHT

Prints error message to stderr, nothing to stdout and return value != 0 if:

Argument count does not equal 2 (e.g. `matrix add m1 m2 m3` or `matrix add m1`).

Argument count is 2 but the file named by either argument is not readable (e.g. `matrix add m1

no_such_file`).

The dimensions of the input matrices do not allow them to be added together following the rules of matrix

addition.

Otherwise, prints the sum of both matricies, in a valid matrix format to stdout, nothing to stderr, and

returns 0.

matrix multiply MATRIX_LEFT MATRIX_RIGHT

Prints error message to stderr, nothing to stdout and return value != 0 if:

Argument count does not equal 2 (e.g. `matrix multiply m1 m2 m3` or `matrix multiply m1`).

Argument count is 2 but the file named by either argument is not readable (e.g. `matrix multiply m1

no_such_file`).

The dimensions of the input matrices do not allow them to be multiplied together following the rules of

matrix multiplication.

Otherwise, prints the product of both matricies, with the first argument as the left matrix and the second

argumentas the right matrix, in a valid matrix format to stdout, nothing to stderr, and returns 0. (`matrix

multiply A B` should return A*B, not B*A)

`

An invalid command must result in an error message to stderr, nothing to stdout, and a return value != 0.

Hints

Try writing each part as a separate function (see the 1.4 bash Functions reading). You can use $1

“${@:2}” to call the function named by argument 1, with the remaining arguments passed to it. For

example, matrix multiply m1 m2 will expand $1 “${@:2}” to multiply m1 m2 inside your script, which will call

the function named “multiply”. This fancy bash method of calling functions would go at the bottom of your

script, after the functions are defined.

You’ll need to use the read command extensively to read in data from a file. Note that it reads in one line

at a time from the stdin buffer and stores the line in a variable called REPLY, unless specified. Generally,

read is used in a while loop, where a file is redirected to stdin of the while loop. Calling read < myfile
multiple times will repeatedly read the first line of myfile.
The expr command and the shell can have conflicts over special characters. If you try expr 5 * ( 4 + 2 ),
the shell will think * is a filename wild card and the parentheses mean command grouping. You have to
use backslashes, like this:
expr 5 \* \( 4 + 2 \)
I highly recommend that you develop this program directly on the class server (os1). Doing so will
prevent you from having problems transferring the program back and forth, which can cause
compatibility issues. Keep in mind that students caught developing on flip risk losing points on the
assignment. If you are using Windows as your operating system, windows may replace newlines in files
with newline-carriage returns. These will be displayed as ^M characters in vim. To remove them, use the
utility dos2unix .
$ dos2unix bustedFile
Consider the following snippet of code. This will allow you to use one variable to hold the path to a file
with passed-in contents, no matter if they came via stdin or via a file specified on the command line:
datafilepath="datafile$$"
if [ "$#" = "1" ]
then
cat > “$datafilepath”

elif [ “$#” = “2” ]

then

datafilepath=$2

fi

Want to remove the last character from a string? Try this:

$ myvar=”abcde”

$ myvar=${myvar%?}

$ echo $myvar

abcd

Want to display all the characters in a file or string, even the non-printing tabs and newlines? Try cat -A

What to Turn in and When

Simply submit your “matrix” script file. Your script must be entirely contained in this one file. Do not split this

assignment into multiple files or programs. As our Syllabus says, please be aware that neither the Instructor

nor the TA(s) are alerted to comments added to the text boxes in Canvas that are alongside your

assignment submissions, and they may not be seen. No notifications (email or otherwise) are sent out when

these comments are added, so we aren’t aware that you have added content! If you need to make a metacomment about this assignment, please include it in a #comment near the top of the script itself, or email the

person directly who will be grading it (see the Home page for grading responsibilities).

The due date given below is the last minute that this can be turned in for full credit. The “available until” date

is NOT the due date, but instead closes off submissions for this assignment automatically once 48 hours

past the due date has been reached, in accordance with our Syllabus Grading Policies.

Grading

148 points are available for your script (which is the only file you’ll submit) successfully passing the grading

script, while the final 12 points will be based on your style, readability, and commenting. Comment well,

often, and verbosely: we want to see that you are telling us WHY you are doing things, in addition to telling

us WHAT you are doing.

The TAs will use this exact set of instructions: Program1 Grading.pdf to grade your submission.

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