Common Linux commands by category

Help and Abbreviations
Command Name	Action
apropos	Finds online manual pages for a specified keyword
info	Displays online help information about a specified command
man	Displays online help information
whatis	Similar to apropos but searches for complete words only
alias	Defines an abbreviation for a long command
type	Shows the type and location of a command
unalias	Deletes an abbreviation defined using alias

Managing Files and Directories
Command Name	Action
cd	Changes the current directory
chmod	Changes file permissions
chown	Changes file owner and group
cp	Copies files
ln	Creates symbolic links to files and directories
ls	Displays the contents of a directory
mkdir	Creates a directory
mv	Renames a file as well as moves a file from one directory to another
rm	Deletes files
rmdir	Deletes directories
pwd	Displays the current directory
touch	Updates a file's time stamp

Find Files
Command Name	Action
find	Finds files based on specified criteria,such as name and size
locate	Finds files using a periodically updated filename database.(The database is created by the updatedb program.)
whereis	Finds files based in the typical directories where executable (also known as binary)files are located
which	Finds files in the directories listed in the PATH enviroment variable

Processing Files
Command Name	Action
cat	Displays a file on standard output (can be used to concatenate several files into one big file)
cut	Extracts specified sections from each line of text in a file
dd	Copies blocks of data from one file to another(used to copy data from devices)
diff	Compares two text files and finds any differences
expand	Converts all tabs into spaces
file	Displays the type of data in a file
fold	Wraps each line of text to fit a specified width
grep	Searches for regular expressions within a text file
less	Displays a text file one page at a time(can go backward,also)
lpr	Prints files
more	Displays a text file,one page at a time(goes forward only)
nl	Numbers all nonblank lines in a text file and prints the lines to standard output
paste	Concatenates corresponding lines from several files
patch	Updates a text file using the differences between the original and revised opy of the file
sed	Copies a file to standard output while applying specified editing commands
sort	Sorts lines in a text file
split	Breaks up a file into several smaller files with specified size
tac	Reverses a file(last line first and so on)
tail	Displays the last few lines of a file
tr	Substitutes one group of characters for another throughout a file
uniq	Eliminates duplicate lines from a text file
wc	Counts the number of lines,words,and characters for another throughout a file
zcat	Displays a compressed file (after decompressing)
zless	Displays a compressed file one page at a time(can go backward also)
zmore	Displays a compressed file one page at a time

Archiving and Compressing Files
Command Name	Action
compress	Compresses files
cpio	Copies files to and from an archive
gunzip	Decompresses files compressed with GNU Zip(gzip)
gzip	Compresses files using GNU Zip
tar	Creates an archive of files in one or more directories(originally meant for archiving on tape
uncompress	Decompresses files compressed with compress

Managing System
Command Name	Action
bg	Runs an interrupted process in the background
fg	Runs a process in the foreground
free	Displays the amount of free and used memory in the system
halt	Shuts down Linux and halts the computer
kill	Sends a signal to a proces(usually used to terminate a process)
ldd	Displays the shared libraries needed to run a program
nice	Runs a process with lower priority(referred to as nice mode)
ps	Displays a list of currently running processes
printenv	Displays the current enviroment variables
pstree	Similar to ps bu shows parent-child relationships clearly
reboot	Stops Linux and then restart the computer
shutdown	Shuts down Linux
top	Displays a list of most processor-and memory-intensive processes
uname	Displays information about the system and the Linux kernel

Managing Users
Command Name	Action
chsh	Changes the shell(command interpreter)
groups	Prints the list of groups that include a specified user
id	Displays the user and group ID for a specified user name
passwd	Changes the password
su	Starts a new shell as another user or root(when invoked without any argument)

Managing the File System
Command Name	Action
df	Summarizes free and available space in all mounted
du	Displays disk usage information
fdformat	Formats a diskette
fdisk	Partitions a hard disk
fsck	Checks and repairs a file system
mkfs	Creates a new file system
mknod	Creates a device file
mkswap	Creates a swap space for Linux in a file or a hard drive partition
mount	Mounts a device(for example,the CD-ROM)on a directory in the file system
swapoff	Deactivates a swap space
swapon	Activates a swap space
sync	Writes buffered(saved in memory) date to files
tty	Displays the device name for the current terminal
unmount	Unmounts a device from the file system

Dates and Times
Command Name	Action
cal	Displays a calendar for a specified month or year
date	Shows the current date and time or sets a new date and time

Linux 第二天 来点开胃小菜

Combining shell commands
For example,suppose that you want to find out whether a device file name sbpcd resides in your system's /dev directory because some documentation says you need that device file for a Sound Blaster Pro CD-ROM drive.You can combin ls and grep command :

ls /dev | grep sbpcd


Controlling command input and output

Task	Command Syntax
Send stdout to a file	command > file
Send stderr to a file	command 2> file
Send stdout and stderr to a file	command > file 2>&1
Read stdin from file	command < file
Read stdin from file.in and Send stdout to file.out	command < file.in > file.out
Append stdout to the end of a file	command >> file
Append stderr to the end of a file	command 2>> file
Append stdout and stderr to the end of a file	command >> file 2 >&1
Read stdin from the ketboard until the character c	command << c

Another interesting use of sending stdout to a file is the use of the cat command to quickly prepare small text files.For example,suppose that you want to create a new text file where you want to keep storing lines of text you type until you type ZZ and press enter.Here is  how you can accomplish that task:
cat <<zz > input.txt


Typing less with automatic command completion
Many commands take a filename as an argument.To view the contents of the /etc/modprobe.conf text file,for example,type the following command:
cat /etc/modprobe.conf
You can use a bash feature to avoid having to type the whole filename. All you have to type is the bare minimum -- just the first few characters -- to uniquely identify the file in its directory.
To see an example,type cat /etc/mod but don't press Enter;press Tab instead.bash automatically completes the filename,so the command becomes cat /etc/modprobe.conf.Now press Enter to run the command.

Going wild with asterisks and question marks

• The asterisk(*) character matches zero or more characters in a filename. That means * denotes all files in a directory.
• The question mark(?) matches any single character. If you type test?, that matches any five-character text that begins with test.
• A set of characters in brackets matches any single character from that set. The string [aB]*,for example,matches any filename that starts with a or B.

Repeating previously typed commands

To see the command history, type history. bash displays a numbered list of the old commands,including those that you entered during previous logins. bash stores up to 500 old commands.

If the command list is too long,you can limit the number of old commands that you want to see. For example,to see only the ten most recent commands, type this command:

history 10

To repeat a command from the list that the history command shows,simply type an exclamation point(!), followed by that command's number. To repeat command number 3, type !3. Also you can type !more to repeat previously recent more command.

Often, you may want to repeat the last command that you just typed,type two exclamation point as follows:

!!

Sometimes, you may want to repeat the previous command but add extra arguments to it. Sippose that ls -l shows too many files. Simply repeat that command but pipe the output through the more command as follows:

!! | more

Linux 第一天

第一天当然是 ls 命令啦

ls [options] [names]

List contents of directories. If no names are given,list the files in the current directory.

The most useful options include -F, -R, -l, and -a. Some options don't make sense together(e.g.,-u and -c).

Options

-F,--classify,--indicator-style=classify

Flag filenames by appending:

/ to directories

* to executable

@ to symbolic links

| to FIFOs

= to sockets

-R,--recursive

List directories and their contents recursively

-l,--format=long,--format=verbose

Long format listing(includes permissions,owner,size,modification time,etc.).

for example:

total 36

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Desktop

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Documents

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Downloads

-rw-r--r-- 1 royer royer 167 2010-03-07 19:36 examples.desktop

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Music

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Pictures

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Public

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Templates

drwxr-xr-x 2 royer royer 4096 2010-03-07 19:42 Videos

This listing shows considerable information about every directory entry --- each of which can be a file or another directory. Looking at a line from the right column to the left,you see that the rightmost column shows the name of the directory entry.The date and time before the name show when the last modifications to that file were made.To the left of the date and time is the size of the file in bytes.

The file's group and owner appear to the left of the column that shows the file size.The next number to the left indicates the number of links to the file.(A link is like a shortcut in Windows.)Finally,the leftmost column shows the file's permission settings,which determine who can read,write,or execute the file.

The first letter of the leftmost column has a special meaning,as the following list shows:

• l,the file is a symbolic link to another file.In other words,it's a shortcut to something else.
• d,the file is directory.It will appear as a folder in GUI.
• -,the file is normal.
• b,the file represents a block device,such as a disk drive.
• c,the file represents a character device,such as a serial port or a terminal.

After that first letter,the leftmost column shows a sequence of nine characters, which appear as rwxrwxrwx when each letter is present.Each letter indicates a specific permission.A hyphen (-) in place of a letter indicates no permission for a specific operation on the file.Think of these nine letters as three groups of three letters (rwx), interpreted as follows:

• the leftmost group of rwx controls the read,write and execute permission of the file's owner.Although executable programs(including shell programs) typically have execute permission,directories treat execute permission as equivalent to use permission: A user must have execute permission on a directory before he or she can open and read the contents of the directory.
• The middle three rwx letters control the read,write and execute permission of any user belonging to that file's group.
• The rightmost group of rwx letters controls the read,write and execute permission of all other users(collectively thought of as the world).

Thus,a file with the permission setting rwx------ is accessible only to the file's owner,whereas the permission setting rwxr--r-- makes the file readable by the world.

-a,--all

List all files,including the normally hidden files whose names begin with a period.

-A,--almost-all

List all files,including the normally hidden files whose names begin with a period.Does not include the . and .. directories.

-h,--human-readable

Print sizes in kilobytes and megabytes