Shell (3) redirection .doc

1)



Redirection error:

>>>
Cannot redirect
Stderr
, Use
2>
2>
Error redirection

 

2)



Redirection at the same time
Stdout

,
Stderr

:

Xxx 1> a.txt 2> a.txt

Or
Xxx
&> A.txt

Or
Xxx
> & A.txt

 

3)



Redirect to file descriptor:

Use
&
:

> & N

Eg:> & 2
Redirect
Stderr

 

4)



Permanent redirection in the script:

Exec
1> t.txt

Exec
1> t.txt
#

Append
>

Exec
0 <t.txt

Do not have spaces on either side of the redirection symbol

The script can be opened at the same time.
9
File descriptors, which can be customized
3
~
8

Exec
3> t.txt

Echo
"ABC"> & 3 #

Output
T.txt

 

5)



Storage and recovery of descriptors:

Exec 4> & 1
#
Storage
1
To
4

Exec 1> a.txt

#
Set
1

Echo "BBBB"
#
Output
A.txt

Exec 1> & 4
#
Restore
1

Echo "aaaa"> & 1
#
Output
Stdout

 

Similarly:

Exec 4 <& 0
#
Storage
0
To
4

Exec 0 <A. In
#
Redirect Input

Exec 0 <& 4
#
Restore
Stdin

 

6)



Readable and writable file descriptor:

Exec 3 <> a.txt

#3
Can be used for both input and output

 

Exec 3> &-

#
Close
3

 

Eg:

Exec 4> & 1

Echo "BBBB"> & 4
#
Output
Stdout

Exec 4> &-

Echo "aaaa"> & 4
#
Will report an error

 

7)



Redirection of the output of the entire function

You can add redirection directly after the function call.

 

8)



Appendix:

Lsof, view all FD in the Linux System

Lsof-p pid, view all FD of a PID