Scripting : Exercise 2

Hacker Girl
  1. Unix Shell Scripting
  2. Shell Basics
  3. Testing in bash
  4. Capturing User Input
  5. Scripting : Exercise 1
  6. Debugging
  7. Bourne/Bash/Korn Commands
  8. Shell Variables
  9. IO Redirection
  10. Pipes
  11. Operators, Wildcards and Expressions
  12. Flow Control
  13. Scripting : Exercise 2
  14. Shell Differences
  15. String Functions
  16. awk
  17. xargs
  18. Power Tools
  19. Exercise 3


For our first trick, we’re going to write a script that shows us how arguments are dealt with by scripts. Start a new script called args. (Notice that it doesn’t have to be “”.)

Create the script:

if [ $# -lt 1 ] ; then
echo "You must pass at least one argument."
exit 1

Save it, chmod it, and test it by calling it with zero, one and multiple arguments.

Count and echo arguments by adding these lines to the file:

echo "You passed $# arguments."
echo "They are: $*."

Once again, save and test. Try at least one argument that contains one or more spaces. What happens with that argument?

Now add these lines to echo each argument on a separate line:

for x in "$@"
echo "$x"

Usual routine: save and test. Again, use at least one argument containing spaces. How does this script handle them now?

Log Rotation

Assume you will need a script to rotate your log files. The main log is users.log.

Also assume you will keep old log files named users.log.1 through users.log.5. They will live in in /var. DON’T CREATE THEM DIRECTLY. Do it in the script.

Write a new script that renames file users.log to users.log.2, and so forth, and deletes or overwrites the oldest log.

Name it rotate.

Make sure it is executable.

You can use this procmail rotation script as a model:

# Rotate procmail log files
cd /home/studenth/Mail
rm procmail.log.6 # This is redundant
mv procmail.log.5 procmail.log.6
mv procmail.log.4 procmail.log.5
mv procmail.log.3 procmail.log.4
mv procmail.log.2 procmail.log.3
mv procmail.log.1 procmail.log.2
mv procmail.log.0 procmail.log.1
mv procmail.log procmail.log.0

Now update your script to take an argument, rather than a hard-coded name, for the log names.