Connecting and expanding commands
A truly powerful feature of the shell is the capability to redirect the input and output of commands to and from other commands and files. To allow commands to be strung together,the shell uses metacharacters. As noted earlier, a metacharacter is a typed character that has special meaning to the shell for connecting commands or requesting expansion.
Piping commands
The pipe (|) metacharacter connects the output from one command to the input of another command. This lets you have one command work on some data, and then have the next command deal with the results. Here is an example of a command line that includes pipes:
$ cat /etc/passwd | sort | cut -f1,5 -d: | less
This command lists the contents of the /etc/passwd file and pipes the output to the sort command. The sort command takes the user names that begin each line of the /etc/passwd file, sorts them alphabetically, and pipes the output to the cut command. The cut command takes fields 1 and 5, with the fields delimited by a colon (:), then pipes the output to the less command. The less command displays the output one page at a time, so that you can go through page by page.
Using file-matching metacharacters
To save you some keystrokes and to be able to refer easily to a group of files, the bash shell lets you use metacharacters. Anytime you need to refer to a file or directory, such as to list it, open it, or remove it, you can use metacharacters to match the files you want. Here are some useful metacharacters for matching filenames:
• * — This matches any number of characters.
• ? — This matches any one character.
• [...] — This matches any one of the characters between the brackets, which can
include a dash-separated range of letters or numbers.
Sample Examples:
Using file-redirection metacharacters
Commands receive data from standard input and send it to standard output. Standard input is normally user input from the keyboard, and standard output is normally displayed on the screen. Using pipes (described earlier), you can direct standard output from one command to the standard input of another. With files, you can use less than (<) and greater than (>) signs to direct data to and from files. Here are the file redirection characters:
• < — Direct the contents of a file as input to the command (because many commands take a file name as an option, the < key is not usually needed).
• > — Direct the output of a command to a file, overwriting any existing file.
• >> — Direct the output of a command to a file, adding the output to the end of the existing file.
Here are some examples of command lines where information is directed to and from files.
Managing background and foreground processes
If you are using Linux over a network or from a dumb terminal (a monitor that allows only text input with no GUI support), your shell may be all that you have. You may be used to a windowing environment where you have a lot of programs active at the same time so that you can switch among them as needed. This shell thing can seem pretty limited.
There are several ways to place an active program in the background. One mentioned earlier is to add an ampersand (&) to the end of a command line. Another way is to use the at command to run commands in a way in which they are not connected to the shell. (See Chapter 12 for more information about the at command.)
To stop a running command and put it in the background, press Ctrl+z. After the command is stopped, you can either bring it to the foreground to run (the fg command) or start it running in the background (the bg command).
# ls -l drwxrwxrwx 2 sam adm 4096 10月 30 20:14 file6 -rwxrwxrwx 2 sam adm 0 10月 31 01:01 http3.conf -rwxrwxrwx 2 sam adm 0 10月 31 01:01 httpd.conf
# find . -perm -7 -print | xargs chmod o-w # ls -l drwxrwxr-x 2 sam adm 4096 10月 30 20:14 file6 -rwxrwxr-x 2 sam adm 0 10月 31 01:01 http3.conf -rwxrwxr-x 2 sam adm 0 10月 31 01:01 httpd.conf
用grep命令在所有的普通文件中搜索hostname这个词：
# find . -type f -print | xargs grep "hostname" ./httpd1.conf:# different IP addresses or hostnames and have them handled by the ./httpd1.conf:# VirtualHost: If you want to maintain multiple domains/hostnames on your
用grep命令在当前目录下的所有普通文件中搜索hostnames这个词：
# find . -name \* -type f -print | xargs grep "hostnames" ./httpd1.conf:# different IP addresses or hostnames and have them handled by the ./httpd1.conf:# VirtualHost: If you want to maintain multiple domains/hostnames on your
By default, MySQL Server will be installed with root superuser without any password. You can connect to MySQL server as root without requiring password or by keying in blank password. However, if you have set the password for root and forget or unable to recall the password, then you will need to reset the root password for MySQL.
Login as root to the Unix-like (Unix, Linux or BSD) machine with the MySQL server.
Stop the MySQL server by using either of the following command
#/etc/init.d/mysql stop
Now you need to Start MySQL server without password
# mysqld_safe --skip-grant-tables &
Connect to mysql server using mysql client with the following command
# mysql -u root
Now you should be having mysql prompt
mysql>
Now you need to Setup new MySQL root user password
mysql> use mysql;
mysql> update user set password=PASSWORD(“newrootpassword”) where user=’root’;
mysql> flush privileges;
mysql> quit
Note: Replace newrootpassword with the new root password for MySQL server. Flush Privileges is needed to making the password change effect immediately.
Now you need to Stop MySQL Server using the following command
# /etc/init.d/mysql stop
Test Your New Mysql root password
First you need to start mysql server using the following command
# /etc/init.d/mysql start
# mysql -u root -p
Now it will prompt for root password and enter your new root password
My previous reference for practical Linux commands was surprisingly popular with over 3.5 million hits in nearly 5 years. So I've decided to start compiling another list of somewhat more involved/esoteric commands. Examples marked with • are valid/safe to paste without modification into a terminal, so you may want to keep a terminal window open while reading this so you can cut & paste.
This is a linux command line reference for common operations.
Examples marked with • are valid/safe to paste without modification into a terminal, so
you may want to keep a terminal window open while reading this so you can cut & paste.
All these commands have been tested both on Fedora and Ubuntu.
See also more linux commands.
Command
Description
•
apropos whatis
Show commands pertinent to string. See also threadsafe
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