Mkfifo, EXEC commands under Linux are used

Mkfifo
section:user Commands (1)
updated:1998 Year November
Index Return to Main Contents
Name (title)
Mkfifo-Create FIFO (named pipe)
Synopsis (Overview)
mkfifo [options] File ...

POSIX Options (option): [-M mode]

GNU options (Shortest form): [-M mode] [--help] [--version] [--]
DESCRIPTION (description)
Mkfifo creates a FIFO (also known as a named pipe) with the specified file name.

A "FIFO" is a special type of file that allows independent processes to communicate. A process opens a FIFO file for write operations, while another process reads it, and the data can be executed as well as the anonymous pipeline common in the shell or elsewhere.

by default, the FIFO mode that is created is 0666 (' a+rw ') minus the bits set in the umask.
options (optional)

-M mode,--mode=mode
set the mode of the FIFO that is created to mode, which can be a symbol pattern in chmod (1) and use the default mode as the starting point.


GNU Standard options (GNU std option)

--help
prints a usage message on the standard output and exits in a successful state.  
--version
Prints the version information on the standard output and exits in a successful state.  
--  
terminates the list of options.  

Summary of exec usage in Linux

EXEC Related: http://blog.csdn.net/cyberrusher/article/details/7253385

Summarize a table first:

EXEC Command	Role
exec ls	in shell ls ls after the end shell
EXEC <file< span= "" >	Use the content in file as the standard input for exec
EXEC >file	Write the contents of file as standard
EXEC 3<file< span= "" >	Read file into fd3
Sort <&3	the content read in FD3 is categorized
EXEC 4>file	writes content written to fd4 to file
LS >&4	Ls will not have a display, directly written to the fd4 , that is, the above file
EXEC 5<&4	Create a copy of the fd4 fd5
EXEC 3<&-	Close fd3

1. Exec Execution Program

Althoughexecand theSourceis executed directly in the parent process, butexecthis andSourceThere's a big difference,Sourceis to performShellscript, and will return to the previousShell. andexecexecution does not return to the previousShell, but directly to the previous landingShellas a procedure, it is copied on the line.

To illustrate:

[Email protected]:~/test#exec ls

EXP1 exp5 linux-2.6.27.54 ngis_post.sh test Xen-3.0.1-install

[Email protected]:~/test#exec >text

[Email Protected]:~/test#ls

[Email protected]:~/test#pwd

[Email Protected]:~/test#echo "Hello"

[Email Protected]:~/test#exec>/dev/tty

[Email protected]:~/test#cat text

Exp1

Exp5

linux-2.6.27.54

ngis_post.sh

Test

Text

Xen-3.0.1-install

/root/test

Hello

[Email protected]:~/test#

Exec >text is to open the standard output of the current shell to the text file

[Email Protected]:~/test#cat test

Ls

Pwd

[Email Protected]:~/test#bash

[Email protected]:~/test#exec <test< span= "" >

[Email Protected]:~/test#ls

EXP1 exp5 linux-2.6.27.54 ngis_post.sh Test text Xen-3.0.1-install

[Email protected]:~/test#pwd

/root/test

[Email protected]:~/test#

[Email protected]:~/test#exit # Automatic execution

2. exec redirection

Let's go first. Look in the/dev/fd/directory:

[Email protected]:~/test#cd/dev/fd

[Email Protected]:/dev/fd#ls

0 1 2 255

There are four items by default:0 is the standard input and the default is the keyboard.

1 is the standard output, the default is the screen /dev/tty

2 is a standard error, the default is also the screen

255

When we execute exec 3>test :

[Email protected]:/dev/fd#exec 3>/root/test/test

[Email Protected]:/dev/fd#ls

0 1 2) 255 3

[Email protected]:/dev/fd#

See, more than a 3, that is, added a device, here can also experience the Linux device is the concept of the file. at this time fd3 is the equivalent of a pipeline, and redirects to the fd3 file will be written in test . This redirection can be turned off with exec 3>&-.

[Email protected]:/dev/fd#who >&3

[Email Protected]:/dev/fd#ls >&3

[Email protected]:/dev/fd#exec 3>&-

[Email Protected]:/dev/fd#cat/root/test/te

Test text

[Email Protected]:/dev/fd#cat/root/test/test

Root Tty1 2010-11-16 01:13

Root pts/0 2010-11-15 22:01 (192.168.0.1)

Root PTS/2 2010-11-16 01:02 (192.168.0.1)

0

1

2

255

3

3. Application Examples:

EXEC 3<test< span= "" >

While Read-u 3 pkg

Do

echo "$pkg"

Done

Mkfifo, EXEC commands under Linux are used