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filename
 
where the result produces 
filename
.gz
. The 

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compressed file cannot be viewed until it is decompressed. The decompression algorithm is 
either 
gunzip
or 
gzip –d
and it will remove the .gz extension.
The bzip2 program uses the Burrows–Wheeler sorting algorithm combined with 
Huffman codes for compression. There is a bzip program although it is based on the LZ77 
and LZ78 algorithms. The bzip2 program operates much the same as gzip/gunzip with 
the instruction being 
bzip2 
filename
which creates 
filename
.bz2
. To decompress, 
use either 
bunzip2
or 
bzip2 –d
. As with gunzip, these programs will remove the .bz2 
extension.
There is also a zip program which is used to both bundle and compress files. Its format is 
different because it produces a single bundled file in place of multiple input files.
zip 
destination
.zip 
sourcefile(s)
To unzip, use 
unzip 
filename
.zip
. The zip program uses the DEFLATE compres-
sion algorithm which combines both LZ77 and Huffman codes.
3.9 CHAPTER REVIEW
Concepts and terms introduced in this chapter:
• Absolute path—path from root to directory/file.
• Compression—reducing files’ sizes by either discarding data or replacing data with 
replacement strings.
• Decompression—or uncompression, restoring the file to its original format. Only 
lossless compressed files can be decompressed.
• Device driver—a program that permits the CPU to communicate with a hardware 
device. The driver is installed as part of the operating system.
• Directory—a unit of organization which can contain files, subdirectories, and links.
• File—the basic unit of storage in the logical file system.
• File system—the collection of devices storing the files.
• Home directory—the directory reserved for the given user.
• Link—a pointer to an object in the file system.
• Logical file system—the user’s view of the file system consisting of files, directories, 
paths, and partitions.
• Mounting—the act of making a file system accessible.
• Parent directory—the directory of which the current directory is contained.
• Partition—a logical way to separate groups of directories so that each partition can 
be treated independently.

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• PATH variable—an environment variable which stores the directories that the Bash 
interpreter searches for an executable program when a command is entered.
• Permissions—access control to determine who can read, write, or execute a file or 
directory.
• Physical file system—the physical mechanisms that implement the file system 
including disk drives (and other storage devices); a file is stored in the physical file 
system as a collection of blocks distributed across one or more devices, connected 
by pointers.
• Recursive copy/delete—an operation to copy or delete not just the contents of a direc-
tory, but all subdirectories and their contents.
• Relative path—path specified from the current working directory.
• Top-level Linux directories—a standard collection of directories that help Linux 
users and administrators know where to look.
• Wildcards—characters that can be used in Bash to specify multiple files such as * 
matching all files and ? matching any one character of a file name.
• Working directory—the directory that the user is currently interacting in, reached 
using cd commands.
Linux commands covered in this chapter:
• bzip2/bunzip2—compress/decompress files using Burrows–Wheeler and Huffman 
codes.
• cat—concatenate files; often used to display files’ contents to the terminal window.
• cd—change the working directory.
• chmod—change the permissions of a file.
• comm—compare two sorted files, displaying all differences.
• cmp—compare two files, byte by byte, displaying the point where the two files differ.
• cp—copy one or more files or entire directories to another location.
• cut—remove portions of every line of a file.
• diff—compare two files and display their differences.
• file—output the type of entity passed as a parameter such as a text file, a directory, a 
block device.
• find—locate files in the file system based on some criteria such as name, permissions, 
owner, last access time.

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• gzip/gunzip—compress/uncompress files using LZ77 and Huffman codes.
• head—display the first part of a file.
• join—join lines of files together which have a common value for one of its fields.
• less—display a file screen-by-screen; allows forward and backward movement.
• locate/slocate—locate files in the file system based on name; uses a preestablished 
database of file names.
• ln—create a hard link; creates a symbolic link if you supply it with the option -s.
• ls—list the contents of the given or current directory.
• mkdir—create a new directory.
• more—display a file screen-by-screen; allows only forward movement.
• mv—move one or more files to a new location or rename a file.
• paste—unite files together by fields.
• pwd—print the current working directory.
• rm—delete one or more files; can delete directories if the -r recursive option is used.
• rmdir—delete an empty directory.
• sort—sort the contents of a file.
• split—split a file’s contents into multiple files.
• strings—output sequences of 4 or more printable characters found in non-text-based 
files.
• tail—display the last part of a file.
• touch—create an empty text file.
• uniq—examine a file for duplicated consecutive lines.
• updatedb—create or update the file database as used with locate/slocate.
• wc—perform a character, word, and line count on the given file(s).
REVIEW QUESTIONS
1. Which of the following Linux file system commands can you issue
a. On a directory?
b. On a file?
ls cd mv rm cp sort touch less cat wc chmod

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2. Referring to Figure 3.4, assume you are currently in the directory /
home/foxr/
temp2/a
.
a. Write an absolute path to take you to zappaf.
b. Write a relative path to take you to zappaf.
c. Write an absolute path to take you to etc.
d. Write a relative path to take you to etc.
3. You are user zappaf. You were in the directory /usr and then performed cd /home/
foxr/temp. What values would you find in these environment variables? PWD 
OLDPWD HOME.
4. What is the difference between home/foxr and /home/foxr?
5. What does ~ represent? What does ~zappaf represent?
6. What is the difference between . and ..?
For questions 7 through 16, assume that the current directory contains the following items 
(all of which are files):
abc.txt abc1.txt abb.txt bbb.txt bbb.dat bbb bbbb c123.txt ccc.txt
7. List the files that the following command will display: ls *
8. List the files that the following command will display: ls *.txt
9. List the files that the following command will display: ls a*.*
10. List the files that the following command will display: ls ab?.txt
11. List the files that the following command will display: ls bbb*
12. List the files that the following command will display: ls bbb.*
13. List the files that the following command will display: ls c??.txt
14. List the files that the following command will display: ls [ab][ab][ab].*
15. List the files that the following command will display: ls [a-c]??.???
16. List the files that the following command will display: ls [!c]*
17. Refer back to Figure 3.4. Assume that you are currently in the subdirectory 
temp2
of 
foxr
. Assume the subdirectory 
a
contains five files and subdirectory 
b
is empty.
a. What is the result of doing rmdir a?
b. What is the result of doing rmdir b?
c. What is the result of doing rm -ir a*?
d. How would rm -fr a* differ from rm -ir a* from part c?

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For questions 18 through 21, assume the directory zappaf has the following partial 
long listing:
-rw-rw-r-- zappaf zappaf . . . foo1.txt
-rw-rw-r-- zappaf zappaf . . . foo2.txt
-rw-rw---- zappaf zappaf . . . foo3.txt
18. Write a command, as foxr, to copy these files to foxr’s temp directory.
19. Will your command from 18 successfully copy all three files? Why or why not?
20. For your copy command from #18, what would differ if you added the option -p?
21. How does the command mv ~zappaf/foo1.txt. differ from the command mv ~zappaf/
foo1.txt foo4.txt?
22. The -f option in rm forces a file to be deleted without asking for permission. What 
then does the -f option do for cp?
23. What is the difference between 
tail –n 10
and 
tail –n 
+
10
when issued on a 
file of 100 lines?
24. What is the difference between 
tail –c 10
and 
tail –n 10
when issued on a 
file of 100 lines and 1000 characters?
25. Assume you have two files that are nearly identical. To view the differences between 
them, which file comparison program should you use?
26. Assume you have two files that are sorted. To view the differences between them, 
which file comparison program should you use?
27. Which of the file comparison programs can compare one file to several other files?
28. How does uniq differ from diff and cmp?
Assume you have two files: names.txt and phone.txt which each contain enumerated 
(numbered) lists of names (names.txt) and phone numbers (phone.txt). We assume that 
the