The pipeline, redirection and regular expression of Linux learning notes

Pipeline: The output of the previous command, as input to the latter command

Command 1 | command 2 | command 3| command 4  

#tee that is displayed on the monitor, and the file is saved in the file

Example #echo "Hello, word" | Tee/tmp/hello.out

Example #wc-l/etc/passwd | Cut-d '-f1

I/O redirection

> output redirection, overwrite output

> > Append Output

#set-C Disables overwrite redirection for existing files, forcing overwrite of output, using >|

#set +c Turn off the above features  

2>: Redirect Error output

2 >>: Append redirect Error output

Example: #ls/varr>/tmp/var.out 2>/tmp/var.out, correct output and error output overwrite/tmp/var.out file  

&>: Redirect standard output or error output to the same file  

< input redirection,

Example: # tr ' A-Z ' A-Z ' </tmp

<< Append Input

Example 1: #cat >>/tmp/file.txt <<eof: Save keyboard input to File.txt

Example 2: #cat <<eof

d| D Show Delect

U|u Show UID

EOF: Display the content information in the script

Regular Expressions: Regular expression, REGEXP

Basic REGEXP: Basics

Extended REGEXP: Extended

Basic Regular Expressions:

Metacharacters

. Any single character

Example #grep ' r.. T '/etc/passwd

* The number of previous character matches

. * matches any character of any length

\？ Match its preceding character 1 or 0 times

\{m,n\} indicates that the preceding character appears at least m times and at most n times

Position Lock:

^: Anchor the beginning of the line, any content after this character must appear at the beginning of the line

Example: grep ' ^r. T '/etc/passwd

$:: Anchor line end, any content in front of this character must appear at the end of the row

Example: grep ' b$ '/etc/passwd

^$: Blank Line

Example: grep ' [[:d igit:]] '/etc/inittab

\< or \b: Indicates that any subsequent character must appear as a word header

\> or \b: Indicates that any character preceding it must appear as the tail of the word

Group

\ (\) \ (ab\) means ab a whole

\1: Indicates the contents of the first opening parenthesis and the corresponding closing parenthesis

example : #grep '. *\ (L. e\). * \1 '/tmp/

Example # grep ' \ ([0-9]\). *\1$ '/etc/inittab

Example: #grep ' ^1\ ([0-9]\): \1.*\1$ '/etc/inittab

To extend the regular expression:

Character matching

. any single character

[] matches any single character within the specified range

[^] matches any single character outside the specified range

Number of Matches

* the number of previous character matches

? match its preceding character 1 or 0 times

+ match the characters in front of it at least once

[M,n] indicates that the preceding character appears at least m times and at most n times

Anchor Point character

^ Anchor The beginning of the line, any content after this character must appear at the beginning of the line

$ Anchor Line end, any content in front of this character must appear at the end of the row

\< indicates that any subsequent character must appear as a word header

\> indicates that any character preceding it must appear as the tail of the word

Group

（）

\1 \2 \3

Or

| : B|a left character or right character

Example: #grep-e--color ' ^[[:space:]]+ '/boot/grub/grub.conf

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The pipeline, redirection and regular expression of Linux learning notes