Redirect, pipe--linux basic commands (6)

1.Output Redirection

Linux The default input is the keyboard, and the output is the monitor. You can use redirection to change these settings. For example , when using the WC command to manually enter a text to calculate the number of characters, you can directly put a written file with '<' point to this command, You can directly count the number of characters in this file.

STDOUT(standard output) and STDERR(standard error) can be redirected to a file

Command Operation Symbols file name

Supported operational symbols include:

> put STDOUT redirect to file

,etc under the passwd file,the app does not have a passwd file, the two redirects to export them to the file ls.txt , Only the wrong one is left after the carriage return. Then we look at the Ls.txt file and find the correct standard output inside

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2> put STDERR redirect to file

Similarly, the use of 2> will be displayed correctly, the error output to the Ls.txt file.

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&> redirect all output to file (or > 2>&1 )

, both methods input the correct error into the file.

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It is important to note that using > overrides the file contents by default.

Use set-c prevents content from being overwritten by existing files , but can be appended

>> On the basis of the original content, Append Content

>|file Force Overwrite

Set +c Allow overwrite

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You can also direct output and errors to different locations at one time, respectively

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, directed to the Right.txt and error.txt files, respectively.

2.trConvert and delete

TR [OPTION] ... SET1 [SET2]

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(Enter the condition first, then enter the content you want to convert, enter a line of output line, until CTRL + C exit)

You can also use the redirect function, do not need input, enter a file directly, you can be replaced

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, you can output the. BASHRC content without having to re-BASHRC the contents of the. (This operation does not change the contents of the. bashrc.) )

- C – C--complement the complement of a character set (that is, nothing is removed)

, the characters except C are replaced by a.

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- d --delete Delete all characters belonging to the first character set

, all of the files in the ABC have been removed.

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- s --squeeze-repeats to remove consecutive repetitions of characters into one character

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, turn the repeating ABC into one, and the rest of the repeating letters do not move.

- T --truncate-set1 converts the character of the first character set to the second character set (no substitution is made on the corresponding one)

The corresponding character

[: Alnum:] : Letters and Numbers

[: Alpha:] : Letters

[: Cntrl:] : Control (non-printing) characters

[:d Igit:] : Digital

[: Graph:] : Graphic characters

[: Lower:] : Lowercase Letters

[:p rint:] : Printable characters

[:p UNCT:] : Punctuation

[: Space:] : white space characters

[: Upper:] : Uppercase Letters

[: Xdigit:] : Hexadecimal characters

3.Import from FileStdin

in the same way, we can use < to redirect the standard input Stdin

Some commands can accept import from a file Stdin

tr ' A-Z ' A-Z ' </etc/issue This command converts lowercase characters in /etc/issue to uppercase characters.

tr–d ABC </etc/fstab This command removes any characters from all of the ABC in the Fstab file (these two functions have been used above)

cat> file can write content to a file

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Press ctrl+d or Ctrl + C to leave, you can use the file instead of the keyboard input

<< terminating words

You can edit it as you wish, until a line has only that terminating word, and you exit the edit and send the above content to the file.

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Until the last act! Automatically exits when the

Cat > Filea < Fileb

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to write the contents of the Text.txt to file.txt

Again, we can import the file into the message and send it in this way.

( the code for sending the message is the mail-s " message name " that you want to send to, and then you enter the content and use ctrl+d Exit )

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Now we will Text.txt This file is written to the message and sent:

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, login magedu user, enter mail to view the mail, found that the message received is text.txt letter. (Enter quit after reading )

4.Piping

pipe (using symbols " | "representation" is used to connect commands

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, Pass the 1+2 to the calculator and draw the result

Command 1 | Command 2 | Command 3 |  ... .. Send STDOUT of command 1 to STDIN of command 2, STDOUT of command 2 to command 3 The STDIN.

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, Will | Used in conjunction with tr to turn all the repeating spaces into a single space.

then continue to use | and grep command (which will be discussed later) query /boot that line

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| only correct results can be redirected to the next command

using 2>&1 | or |& can redirect all results

5.REDIRECT to multiple targetsTee

command 1 | tee [ -A] file name | command 2

Save the STDOUT of command 1 in the file as input to command 2

-A append

Use:

save output at different stages

Troubleshooting Complex Pipelines

view and record output at the same time

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Redirect, pipe--linux basic commands (6)