Linux file management and text one of the Three Musketeers grep, and the use of regular

1: File Permissions

There are three types of user access to a file: R (Read), W (write), X. It's a little different for files and directories.

File:

R: Use the text View tool to view its file contents.

W: Use the text Editing tool to edit its file contents.

X: You can request this file to run as a city execution to the kernel.

Directory:

R: You can use the LS command to list files under Subdirectories and files.

W: You can create and delete files in this directory.

X: You can use the ' ls-l ' command to list the file attributes of the directory and subdirectories, and you can use the CD to switch the working directory to a directory.

File permissions are primarily defined for three types of objects.

Owner: Master, group: Genus, Other: other users.

Three commands for Rights management

Change file belongs to group: CHGRP Group name File name

If the file test belongs to the test group change to the Admin group, the command is: CHGRP admin test.

-r: Represents a cascade change to the owning group of sub-files and subdirectories in this directory.

Document owner management: Chown

If the file test belongs to test, it is the main CentOS chown CentOS test.

-R: Also represents a cascading change.

The owning and owning group of the Cascade change file

Chown-r user name: The owning group file name.

Change the file's ownership limit Chmod:r=4,w=2,x=1

chmod [-r] XYZ file permissions.

The first type of change:

If you change the Cascade change file, test is the master for read-write only execute permissions, the group is read permission, and the other is the EXECUTE permission. Chmod-r u=wrx,g=wr,o=x Test

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Second change: You can use +WRX, or-WRX +: to indicate an increase in permissions, which means to remove the permissions you have.

Chmod-r U-WR,G+X,O+WR Test

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Third change: 7=wrx r=4,w=2,r=1 with digital permissions 0 means no permissions.

Chmod-r 701 Test

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The default permission for a directory is 755, and the permission for a file is 644

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The default permissions for a file depend on the Umask value

Umask: Represents the default value of the current user's permissions when creating a new file or directory.

Enter the default permission value that the Umask command is currently losing.

By default, the rule

1: The default maximum permission of 666 is U=WR,G=WR,O=WR when creating a file. One less enforcement privilege is due to security considerations and the file start-up cannot be executed.

2: When creating a directory, the directory has execute permissions because it is going to the directory, so the maximum permissions for the directory are 777.

Defines a umask value of 002

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Because the Umask 002 value is defined. Because the highest permission to create a file is 666, the default initial permissions are:

U, is the main WR-0=WR representative has read and write permission, G belongs to the group wr-0 =WR Read and Write permissions, the other user and group permissions for Rw-w=r only Read permissions, this is the creation of files.

When creating a directory, because the most permission to create the directory is 777, so the owner: Wrx-0=wrx owns WRX, the group WRX-0=WRX has the WRX,O=RWX-X=RW has the RX permission.

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If the value of Umask is 003 then for the creation of the file is the main RW, belong to the group RW other user rw-w=r value.

If the value of Umask is 005 then the file carcass is the main RW, which belongs to the group RW, and the other user rw-r=w. Because there is no execution permission by default, you must remove the Execute permission. For example 003 The last 3 of the theoretical authority for WX, because there is no execution permissions so the actual permission is W, minus the W so R, so the end of the other user and group permissions for the R permission.

2: Text One of the Three Musketeers use of grep

The Three Musketeers of Linux text Processing.

grep: Text Filtering tool.

Sed: text editor.

awk: Text Report Generator.

Grep:global search REgular expression and print out of the line based on the global regular representation of the matching-to-row printing tool.

Pattern: The filter condition written by the metacharacters of the regular expression and the text characters.

Metacharacters: A character does not represent its literal meaning, but is used to denote a wildcard or control function.

The regular is divided into two categories:

Basic Regular Expressions: BRE

Extended Regular expression: ERE

grep [option] PATTERN file:

--color: The matching to the string to do highlighting;

-V: Displays the rows that the pattern does not match.

-I: Ignore case.

-O: Displays only the strings that can be matched to;

-Q: Silent mode.

The grep family has three commands:

grep: basic Regular expression

-e: Extended expression support

-F: Regular expressions are not supported.

Egrep: Extended Expression

Fgrep: Regular expressions are not supported.

The metacharacters of the basic regular expression:

Character Matching:

.: matches any single character.

[]: Match a single character within the established range, such as [0-9] representing any character within 0-9, [a_z] table uppercase any single character within a-Z, [A-z]: Express lowercase letters of any single character.

[^]: Set the non-single character within the range.

Common Special Symbols:

[: Lower:]: represents lowercase characters [a-z]

[: Upper:]: Represents uppercase characters [A-z]

[: Space:]: Represents a blank key.

Number of occurrences that specify the number of occurrences of the preceding character

*: Only occurrences of the preceding character are repeated any time.

\？ : 0 or 1 times. \ represents escape.

\+:1 times or more.

\{m\}: Represents the exact m-time.

\{n,m\}: Represents [N,m] interval times.

\{0,n\}: Up to n times.

\{m,\}: At least m times.

. *: Matches any character of any length.

Location anchoring:

^: Anchor at the beginning of the line.

$: End of line anchoring.

\<,\b: The word header is anchored to the left side of the pattern that represents the word;

\>,\b: The ending anchor is used to represent the right side of the word pattern.

^$: Blank line.

Grouping \ (\)

The content that is matched in the grouping parentheses is recorded by the regular expression engine during execution and saved to the variable. These variables are \1,\2 ...

Back reference: Use a variable to refer to the character to which the pattern in the preceding grouping brackets matches.

Expansion Regular Expression

or expression: | A|b

C|cat: Indicates C or cat, not cat or cat, to write (C|c) at

+: Repeat one or more of the previous regular re

？ : 0 or one of the previous characters.

(): Find the group character

() +: Determination of multiple repeating groups.

1. Display the lines in the/etc/passwd file that end with bash

grep ' bash$ '/etc/passwd

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2. Display the two-digit or three-digit number in the/etc/passwd file

grep ' [0-9]\{2,3\} '/etc/passwd

3. Display lines with ' LISTEN ' followed by 0, one or more whitespace characters in the ' Netstat-tan ' command result

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4. Add user bash, Testbash, basher, and Nologin user (Nologin user's shell is/sbin/nologin), then find the same line in the/etc/passwd file as the user name and its shell name

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5. Display the default shell and UID of root, CentOS, or User1 user on the current system (please create these users beforehand, if not present)

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6, find a word in the/etc/rc.d/init.d/functions file (the middle of the word can be underlined) followed by a set of parentheses line

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7, use echo to output a path, and then egrep find its path base name; Further use Egrep to remove its directory name

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8. Find the number between 1-255 in the result of ifconfig command execution

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Linux file management and text one of the Three Musketeers grep, and the use of regular