[Page 242 (
continued
)]
Chapter Review
Checklist
In this chapter, I described:
-
Bash startup files
-
using shell
variables
-
using aliases, the history mechanism, and command-line editing
-
arithmetic, conditionals, and control structures
-
functions
-
using the directory stack
-
job control
Quiz
|
1.
|
Describe a common use of the built-in variable $$.
|
|
2.
|
What is the
easiest
way to re-execute your ".profile" file?
|
|
|
[Page 243]
|
|
3.
|
Why are braces ( { } ) required around list variables?
|
|
4.
|
Why is the alias mechanism useful?
|
|
5.
|
What
characters
surround an arithmetic expression in a Bash script?
|
|
6.
|
How are functions made available to subshells?
|
|
7.
|
How do you change your command-editing mode from
emacs
to
vim
?
|
|
8.
|
Name
one method used to define a shell variable in a subshell (i.e., pass the value to the subshell).
|
|
9.
|
What shell variable contains the directory stack?
|
Exercises
|
1.
|
Rewrite the loan Perl program from Chapter 4, "GNU Utilities for Power Users" (beginning on page 162) in Bash. [level:
medium
]
|
|
2.
|
Write a utility called
junk
that satisfies the following specification:
|
Utility
:
junk
[-l] [-p] {
fileName
}*
|
|
junk
is a replacement for the
rm
utility. Rather than removing files, it moves them into the subdirectory ".junk" in your home directory. If ".junk" doesn't exist, it is automatically created. The
-l
option lists the current contents of the ".junk" directory, and the
-p
option purges ".junk".
|
Here's an example of junk at work:
$
ls -lG reader.c
...list existing file.
-rw-r--r-- 1 glass 2580 May 4 19:17 reader.c
$
junk reader.c
...junk it!
$
ls -lG reader.c
...confirm that it was moved.
reader.c not found
$
junk badguy.c
...junk another file.
$
junk -l
...list contents of "junk" directory.
-rw-r--r-- 1 glass 57 May 4 19:17 badguy.c
-rw-r--r-- 1 glass 2580 May 4 19:17 reader.c
$
junk -p
...purge junk.
$
junk -l
...list junk.
$ _
|
{% if main.adsdop %}{% include 'adsenceinline.tpl' %}{% endif %}
Remember to comment your script liberally. [level:
medium
]
Projects
|
1.
|
Create a process management utility that allows you to kill processes based on their CPU usage. This kind of utility would be
especially
useful to system administrators (see Chapter 14, "System Administration"). [level:
easy
]
|
|
|
[Page 244]
|
|
2.
|
Write a Bash script called
mv
(which
replaces
the GNU utility
mv
) that
tries
to rename the specified file (using the GNU utility
mv
), but if the destination file exists, instead creates an index number to append to the destination file, a
sort
of version number. So if I type:
$ mv a.txt b.txt
but b.txt already exists,
mv
will move the file to b.txt.1. Note that if b.txt.1 already exists, you must rename the file to b.txt.2, and so on, until you can successfully rename the file to a name that does not already exist. [level:
medium
]
|
|
3.
|
Write a crafty script called
ghoul
that is difficult to kill; when it receives a SIGINT (from a
Control-C
), it should create a copy of itself before dying. Thus, every time an unwary
user
tries to kill a ghoul, another ghoul is created to take its place! Of course,
ghoul
can still be
killed
by a SIGKILL (-9) signal. [level:
hard
]
|
|
