Advanced Bash−Scripting Guide

Lottery Numbers
One type of lottery involves picking five different numbers, in the range of 1 − 50. Write a script that
generates five pseudorandom numbers in this range, with no duplicates. The script will give the
option of echoing the numbers to stdout or saving them to a file, along with the date and time the
particular number set was generated.
Intermediate
Advanced Bash−Scripting Guide
Managing Disk Space
List, one at a time, all files larger than 100K in the /home/username directory tree. Give the user
the option to delete or compress the file, then proceed to show the next one. Write to a logfile the
names of all deleted files and the deletion times.
Safe Delete
Write, as a script, a "safe" delete command, srm.sh. Filenames passed as command−line arguments
to this script are not deleted, but instead gzipped if not already compressed (use file to check), then
moved to a /home/username/trash directory. At invocation, the script checks the "trash"
directory for files older than 48 hours and deletes them.
Making Change
What is the most efficient way to make change for $1.68, using only coins in common circulations
(up to 25c)? It's 6 quarters, 1 dime, a nickel, and three cents.
Given any arbitrary command line input in dollars and cents ($*.??), calculate the change, using the
minimum number of coins. If your home country is not the United States, you may use your local
currency units instead. The script will need to parse the command line input, then change it to
multiples of the smallest monetary unit (cents or whatever). Hint: look at Example 23−4.
Quadratic Equations
Solve a "quadratic" equation of the form Ax^2 + Bx + C = 0. Have a script take as arguments the
coefficients, A, B, and C, and return the solutions to four decimal places.
Hint: pipe the coefficients to bc, using the well−known formula, x = ( −B +/− sqrt( B^2 − 4AC ) ) /
2A.
Sum of Matching Numbers
Find the sum of all five−digit numbers (in the range 10000 − 99999) containing exactly two out of the
following set of digits: { 4, 5, 6 }. These may repeat within the same number, and if so, they count
once for each occurrence.
Some examples of matching numbers are 42057, 74638, and 89515.
Lucky Numbers
A "lucky number" is one whose individual digits add up to 7, in successive additions. For example,
62431 is a "lucky number" (6 + 2 + 4 + 3 + 1 = 16, 1 + 6 = 7). Find all the "lucky numbers" between
1000 and 10000.
Alphabetizing a String
Alphabetize (in ASCII order) an arbitrary string read from the command line.
Parsing
Parse /etc/passwd, and output its contents in nice, easy−to−read tabular form.
Pretty−Printing a Data File
Certain database and spreadsheet packages use save−files with comma−separated values (CSVs).
Other applications often need to parse these files.
Given a data file with comma−separated fields, of the form:
Appendix I. Exercises 435