Redirect, pipe--linux basic commands (6)

Source: Internet
Author: User
Tags lowercase printable characters stdin

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


This article is from the "ty_endless" blog, make sure to keep this source http://tyendless.blog.51cto.com/12435756/1951819

Redirect, pipe--linux basic commands (6)

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