Use of the EXEC command in the shell

As a result of the recent scripting, with exec, haha, today simply record a bit to deepen the impression

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 program, on which the lines are copied

Note: In this case, when executing in a shell script, exec produces a state of exit, so exec is generally invoked, but when it comes to manipulating the file operator, it does not function, and after execution, it continues to remain in the current shell, such as exec 3 <&0 This means that the operator 3 is also pointed to the standard input, have not seen? Okay, now, let's introduce the syntax.

exec
< P class= "P0" style= "MARGIN-TOP:0PT;MARGIN-BOTTOM:0PT;" >exec ls	in shell ls Span style= "font-family: ' The song Body '; >, ls no return to the original after the end shell in the
exec  <>	file exec standard input
exec >file	file
exec 3 <>	file read into fd3 Span style= "font-family: ' The song Body '; >
sort <&3	fd3< Span style= "font-family: ' The song Body '; The content read in is categorized
exec 4>file	will be written to the Span style= "font-family: ' Times New Roman ';" >fd4 file
ls >&4	Ls< Span style= "font-family: ' The song Body '; > There will be no display, write directly to fd4 file in
exec 5<&4	create Span style= "font-family: ' Times New Roman ';" >fd4 fd5
exec 3<&-	close the Span style= "font-family: ' Times New Roman ';" >FD3

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

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>/root/test, and then go to see/DEV/FD, a certain number of 3, what does that mean?It also adds a device that can be realized hereLinuxthe idea of a device as a file. this timefd3is the equivalent of a pipeline, redirected tofd3the files in the file will be written inTestthe. Close this redirect can be usedexec 3>&-

In addition, this command can be used as an option for the Find command, as follows:
(1) in the current directory (including subdirectories), find all txt files and find the line containing the string "bin"
find./-name "*.txt"-exec grep "Bin" {}
(2) in the current directory (including subdirectories), delete all txt files
find./-name "*.txt"-exec rm {}

Let's use it flexibly.

Use of the EXEC command in the shell