Bourne Shell Script Newbie Help
From: Daz (htpw16_at_hotmail.com)
Date: 01/14/04
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Date: 14 Jan 2004 11:24:51 -0800
Hello Group, I need some assistance in starting an assignment. I have
never programmed in Unix let alone shell scripting. I searched the
internet to find similar problems to mine when I came accross this. So
could you aid me in starting this problem. Thank you. Heres the
problem:
Overview
In this assignment you will write a Bourne shell script to calculate
averages and medians from an input file of numbers. This is the sort
of calculation I might do when figuring out the grades for this
course.
The input file will have whole number values separated by tabs, and
each line
of this file will have the same number of values. (For example, each
row
might be the scores of a student on assignments.) Your script should
be able to calculate the average and median across the rows (like I
might
do to calculate an individual student's course grade) or down the
columns (like I might do to find the average score on an assignment).
You should read the paper "Introduction to the Unix Shell" by Bourne
and the man pages on sh, read, expr, cut, head, tail, wc, and sort
before you begin this assignment. These are the utilities that you
will need to write this program.
Your script will be called stats. The general format of the
stats command is
stats {-rows|-cols} [input_file]
Note that when things are in curly braces separated by a vertical bar
it means you should choose one of the things; here for example, you
must choose either -rows or -cols.
The option -rows calculates the average and median across the
rows; the option -cols calculates the average and median
down the columns. When things are in square braces it means they are
optional; you can include them or not, as you choose. If you specify
an
input_file the data is read from that file; otherwise, it is read
from standard input.
Here is a sample run.
Script started on Wed Sep 30 12:07:50 1998
% cat test_file
1 1 1 1 1
9 3 4 5 5
6 7 8 9 7
3 6 8 9 1
3 4 2 1 4
6 4 4 7 7
% stats -rows test_file
Average Median
1 1
5 5
7 7
5 6
3 3
6 6
% cat test_file | stats -c
Averages:
5 4 5 5 4
Medians:
6 4 4 7 5
% echo $?
0
% stats
Usage: stats {-rows|-cols} [file]
% stats -r test_file nya-nya-nya
Usage: stats {-rows|-cols} [file]
% stats -both test_file
Usage: stats {-rows|-cols} [file]
% chmod -r test_file
% stats -columns test_file
stats: cannot read test_file
% stats -columns no_such_file
stats: cannot read no_such_file
% echo $?
1
% exit
Specifications
You must check for the right number and format of arguments to stats.
You should allow users to abbreviate -rows and -cols; any
word beginning with an r is taken to be rows and any word
beginning with a c is taken to be cols. So, for example,
you would get averages and medians across the rows with -r,
-rowwise and -rumplestiltskin. If the command has too many
or two few arguments or if the arguments of the wrong format you
should
output an error message to standard error. You should also output an
error message to standard error if the input file is specified, but it
is not readable.
You should output the statistics to standard output in the format
shown
above. Be sure all error messages are sent to standard error and the
statistics are sent to standard output. If there is any error, the
exit value should be 1; if the stats program runs successfully
the exit value should be 0.
Your stats program should be able to handle files with any reasonable
number of rows or columns. You can assume that each row will be less
than 1000 bytes long (because Unix utilities assume that input lines
will
not be too long), but don't make any assumptions about the number of
rows. Think about where in your program the size of the input file
matters. You can assume that all rows will have the same number of
values; you do not have to do any error checking on this.
You will probably need to use temporary files. For this assignment,
the
temporary files 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 the temporary file uses the
process
id as part of its name, so that there will not be conflicts if the
stats program is running more than once. Be sure you remove any
temporary files when your stats program is done. You should also
use the trap command to catch interrupt, hangup, and terminate
signals to remove the temporary files if the stats program is
terminated unexpectedly.
All values and results are whole numbers. You will use the expr
command to do your calculations; it only works with whole numbers.
When
you calculate the average you should round to nearest whole number.
(How
do you do that with only whole number operations?)
To calculate the median, sort the values and take the middle value.
For example, the median of 97, 90, and 83 is 90. The median of
97, 90, 83, and 54 is still 90--when there are an even number of
values, choose the larger of the two middle values.
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