Chapter Summary

The utilities introduced in this chapter are a small but powerful subset of the many utilities available on a Red Hat Linux system. Because you will use them frequently and because they are integral to the following chapters, it is important that you become comfortable using them.

The utilities listed in Table 5-2 manipulate, display, compare, and print files.

Table 5-2. File utilities

Utility	Function
cp	Copies one or more files (page 129)
diff	Displays the differences between two files (page 135)
file	Displays information about the contents of a file (page 135)
grep	Searches file(s) for a string (page 131)
head	Displays the lines at the beginning of a file (page 132)
lpq	Displays a list of jobs in the print queue (page 131)
lpr	Places file(s) in the print queue (page 131)
lprm	Removes a job from the print queue (page 131)
mv	Renames a file or moves file(s) to another directory (page 130)
sort	Puts a file in order by lines (page 133)
tail	Displays the lines at the end of a file (page 132)
uniq	Displays the contents of a file, skipping successive duplicate lines (page 134)

To reduce the amount of disk space a file occupies, you can compress it with the bzip2 utility. Compression works especially well on files that contain patterns, as do most text files, but reduces the size of almost all files. The inverse of bzip2bunzip2restores a file to its original, decompressed form. Table 5-3 lists utilities that compress and decompress files. The bzip2 utility is the most efficient of these.

Table 5-3. (De)compression utilities

Utility	Function
bunzip2	Returns a file compressed with bzip2 to its original size and format (page 140)
bzcat	Displays a file compressed with bzip2 (page 140)
bzip2	Compresses a file (page 140)
compress	Compresses a file (not as well as gzip) (page 141)
gunzip	Returns a file compressed with gzip or compress to its original size and format (page 141)
gzip	Compresses a file (page 141)
zcat	Displays a file compressed with gzip (page 141)

An archive is a file, frequently compressed, that contains a group of files. The tar utility (Table 5-4) packs and unpacks archives. The filename extensions .tar.bz2, .tar.gz, and .tgz identify compressed tar archive files and are often seen on software packages obtained over the Internet.

Table 5-4. Archive utility

Utility	Function
tar	Creates or extracts files from an archive file (page 141)

The utilities listed in Table 5-5 determine the location of a utility on the local system. For example, they can display the pathname of a utility or a list of C++ compilers available on the local system.

Table 5-5. Location utilities

Utility	Function
apropos	Searches the man page one-line descriptions for a keyword (page 145)
locate	Searches for files on the local system (page 146)
whereis	Displays the full pathnames of a utility, source code, or man page (page 144)
which	Displays the full pathname of a command you can run (page 144)

Table 5-6 lists utilities that display information about other users. You can easily learn a user's full name, the user's login status, the login shell of the user, and other items of information maintained by the system.

Table 5-6. User and system information utilities

Utility	Function
finger	Displays detailed information about users, including their full names (page 147)
hostname	Displays the name of the local system (page 129)
w	Displays detailed information about users who are logged in (page 149)
who	Displays information about users who are logged in (page 147)

The utilities shown in Table 5-7 can help you stay in touch with other users on the local network.

Table 5-7. User communication utilities

Utility	Function
mesg	Permits or denies messages sent by write (page 151)
write	Sends a message to another user who is logged in (page 150)

Table 5-8 lists miscellaneous utilities.

Table 5-8. Miscellaneous utilities

Utility	Function
date	Displays the current date and time (page 137)
echo	Copies its arguments (page 1019) to the screen (page 137)