Some Useful Commands

The tables below list some of the most useful Linux commands. The tables show the command name, what the command does, and where to find more information. In addition, sort and grep, two of the more flexible commands, are documented in this chapter to show the use of complex commands.

Linux commands can be used on the command line or in shell scripts, programs that perform tasks in the Linux shell. Creating shell scripts is discussed in Chapter 19.

Table 7-1. Some Useful Linux File Management Commands

Command	What it does	Details in
cat	Display contents of a file.	Chapter 9
cd	Change current directory.	Chapter 9
chgrp	Change the group owner for a file.	Chapter 9
chmod	Change the permissions of a file.	Chapter 9
chown	Change the owner of a file.	Chapter 9
cp	Copy file or directory.	Chapter 9
diff	Compare the contents of two files.	Chapter 9
diff3	Compare the contents of three files.	Chapter 9
find	Find a file on your hard disk.	Chapter 9
grep	Find a file with specified contents.	Chapter 9
less	Display the contents of a file on the screen, one page at a time.	Chapter 9
ls	List the file names of files in a directory.	Chapter 9
mkdir	Create a new directory.	Chapter 9
mv	Change the location of a file. Can be used to change the name of a file.	Chapter 9
pwd	Show the path to the current directory.	Chapter 9
rmdir	Remove a directory.	Chapter 9
touch	Update the last access/modification dates of a file.	Chapter 9

Table 7-2. Some Useful Linux Account Management Commands

Command	What it does	Details in
env	Set or display environmental variables.	App B
groupadd	Add a new group.	Chapter 8
groups	Display the list of existing groups.	Chapter 8
passwd	Change your password.	Chapter 8
quota	Display used and available disk space for account.	App B
su	Change to the super user or another user account.	Chapter 8
unset	Remove an environmental variable.	App B
useradd	Add a new user account.	Chapter 8
userdel	Delete a user account.	Chapter 8
whoami	Display the current account.	Chapter 8

Table 7-3. Some Useful Linux Print Job Management Commands

Command	What it does	Details in
lpr	Send a file to the printer queue.	Chapter 14
lprm	Remove a file from the printer queue.	Chapter 14
lpq	Display information about the jobs in the queue.	Chapter 14

Table 7-4. Some Miscellaneous Useful Linux Commands

Command	What it does	Details in
whereis	Find the location of a program.	App B
tar	Put files into and retrieve files from an archive file.	Chapter 10
ftp	Transfer files from one computer to another.	App B
clear	Clear the screen.	App B
date	Display the current date and time.	App B
gzip	Compress files.	App B
gunzip	Uncompress files.	App B