Summary of commands for learning Linux (iii)

Permission-related commands and regular expressions

Command chmod

Command format:

chmod [OPTION] ... Mode[,mode] ... FILE ...

chmod [OPTION] ... Octal-mode FILE ...

chmod [OPTION] ...--reference=rfile FILE ...

Role:

Changing the properties of a file

Common parameters:

There are generally three types of file permissions:

U:owner owner

Group of the genus G:group

O:other Other

A:all All

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=mode: =rx;=x

Ug=rx

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"+|-" mode

U+r u+x

Command grep

Command format:

grep [OPTIONS] PATTERN [FILE ...]

grep [OPTIONS] [-E PATTERN |-f file] [FILE ...]

Role:

Text Search tool to search the target text line by row according to the user-specified "mode", printing the matching line

Mode:

Filter conditions written by metacharacters and text characters of regular expressions:

Metacharacters: The character does not represent its literal meaning, it is used to denote the function of the wildcard or control;

Regular expressions are divided into two categories:

Basic Regular Expressions

Extending regular Expressions

grep [OPTIONS] PATTERN [FILE ...]

Options:

--color=auto highlighting the matched string

-V Displays the rows that the pattern does not match

-I ignore character case

-O displays only the string lines that are matched by the pattern

-e using extended regular expressions

Metacharacters

.: Matches any single character

"": matches a single character in any range

"^": matches a single character outside any range

Character Set:

" ": Lower: "" Lowercase letter "": Upper : "" Uppercase letters

"": Alpha: "" "all uppercase and lowercase" ": alnum:" "Numbers plus letters

"": Digit: "" Number "": Space: "" Space "": punct: "" Symbol

Number:

*: Representative Secondary

\？ : 0 or 1 times

\ +: More than 1 times

\{m\}: precise M-times

\{m,n\}: At least m times up to N times

. *: Any length character

Position:

^: Beginning $: Line end \<,\b: \>,\b: Ending

Group:

\(\)

Extending regular Expressions

Character Matching     

.: Matches any single character

"": matches a single character in any range

"^": matches a single character outside any range

Number of Matches

*: Representative Secondary

？ : 0 or 1 times

+: More than 1 times

{m}: precisely M-Times

{M,n}: At least m times up to N times

Position:

^: Beginning $: Line end \<,\b: \>,\b: Ending

Group:

（）

Or:

A|b

Practice:

Show lines ending in bash in the etc/passwd file

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Displays the two-digit or three-digit number in the/etc/passwd file

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Displays lines that end with ' LISTEN ' followed by 0, one, or more whitespace characters in the ' Netstat-tan ' command result

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

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Displays the default shell and UID for root, CentOS, or User1 users on the current system (please create these users beforehand, if not present)

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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 on the line

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Use echo to output a path, then egrep to find its path base name, and further use Egrep to remove its directory name

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

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Summary of commands for learning Linux (iii)