1.2-linux command Help to get detailed

External command: There is an executable program located in a directory of the file system:

Which,whereis

The path to the Shell program search executable file is defined in the PATH environment variable:

# echo $PATH

Note: From left to right

Internal command:

#help COMMAND

External command:

(1) # COMMAND--help

# command-h

(2) User manual (manual)

# Man COMMAND

(3) Information page

# info COMMAND

(4) Help documentation for the program itself

Readme

INSTALL

ChangeLog

(5) Official program document

Official site: Documentation

(6) Official documents of the release version

(7) Google

Internal commands help get the way:

# Help COMMAND

Hash command:

The path result of the shell's search for external commands is cached into the KV (Key-value) store

[[email protected] ~]# hash

Hits command

1/sbin/service

1/bin/cat

2/usr/bin/elinks

1/bin/vi

Hits: Cache Hit

When the command is found in the cache, this value is +1

[email protected] ~]# ls #第一次使用ls命令

Anaconda-ks.cfg Install.log Install.log.syslog

[[email protected] ~]# hash

Hits command

1/sbin/service

1/bin/cat

2/usr/bin/elinks

1/bin/vi

1/bin/ls

[Email protected] ~]# mv/bin/ls /usr/bin/ls #将ls命令移动到/usr/bin/ls

[email protected] ~]# ls #再次输入ls命令提示如下:

-bash:/bin/ls: No file or directory

[Email protected] ~]# echo $PATH

/usr/lib64/qt-3.3/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

[[email protected] ~]# hash

Hits command

1/sbin/service

1/bin/cat

2/usr/bin/elinks

1/bin/mv

1/bin/vi

2/bin/ls #在缓存当中找而不是在PATH当中找

[[Email protected] ~]# type hash

Hash is a shell builtin #hash是一个内部命令

[[email protected] ~]# help hash

Hash:hash [-LR] [-P pathname] [-DT] [name ...]

Remember or display program locations.

Determine and remember the full pathname of each command NAME. If

No arguments is given, information on remembered commands is displayed.

Options:

-D Forget the remembered location of each NAME

-l display in a format that is reused as input

-P Pathname Use pathname are the full pathname of NAME

- R Forget all remembered locations

-T print the remembered location of each NAME, preceding

Each location with the corresponding NAME if multiple

NAMEs is given

Arguments:

name each name are searched for in $PATH and added to the list

of remembered commands.

Exit Status:

Returns success unless NAME is not found or a invalid option is given.

[Email protected] ~]# hash-r #清除缓存当中所有记录

[[email protected] ~]# ls

Anaconda-ks.cfg Install.log Install.log.syslog

[[email protected] ~]# hash

Hits command

1/usr/bin/ls

History command:

What is the role? What are the relevant environment variables? Useful options?

Manage Command history:

When you log in to the shell, the commands that are recorded in the command history file are read: ~/.bash_history

After logging into the shell, the newly executed command is only recorded in the cache. These commands are "appended" to the command history file when the user exits

History

-A: Append the newly executed command history list to the history file in this session

-D: Delete the command specified in history

-C: Empty command history

Quick action:

!n: Invoking the nth command in history

!string: Call the last command in history that starts with a string

!! : Call the previous command

External commands help get the way:

(1) COMMAND--help

[[Email protected] bin]# type grep

grep is/bin/grep

[[email protected] bin]# grep--help

Usage: grep [options] ... PATTERN [FILE] ...

Find the PATTERN in each FILE or standard input.

The default PATTERN is a basic regular expression (abbreviated to BRE).

For example: Grep-i ' Hello World ' menu.h main.c

Regular expression Selection and interpretation:

-E,--extended-regexp PATTERN is an extensible regular expression (abbreviated as ERE)

-F,--fixed-strings PATTERN is a set of fixed-length strings separated by a break character.

-G,--basic-regexp PATTERN is a basic regular expression (abbreviated as BRE)

-P,--perl-regexp PATTERN is a Perl regular expression

-E,--regexp=pattern using PATTERN for matching operations

(2) Man COMMAND

Manual page:/usr/share/man

Man1...man8

Man1: User Commands

Man2: System call

MAN3: library Call

MAN4: Equipment files and special files

MAN5: Configuration file format

MAN6: Game-related

MAN7: Miscellaneous

MAN8: Commands for managing classes

Note: Some keywords exist in more than one section of the Help manual, to view the manuals in the specified chapters: Man n COMMAND

Configuration file for man command:/etc/man.config

Manpath:/path/to/somewhere: Indicates the new manual file search location

# man-m/path/to/somewhere Command: Searches the command command's hand pages to the specified location and displays

The paragraph description in the Help manual:

Name: program names and brief description

Sysnopsis: Commands use brief help

DESCRIPTION: A detailed description of the function

Options: Option

EXAMPLES: Using the example

AUTHOR: Author

REPORTING BUGS:

See ALSO:

Sysnopsis:

[]: Optional content

<>: Optional content

A|b: Two Choose one

... : The same content can appear multiple times

How to operate the man command: (call less command)

SPACE,CTRL+V,CTRL+F,CTRL+F: Flip the screen to the end of the file

B,CTRL+B: Flip the screen to the file header

D,ctrl+d: Turn half screen at the end of the file

U,ctrl+u: Turn half screen to file header

RETURN or ^n or E or ^e or J or ^j: Turn 1 lines at the end of the file

Y or ^y or ^p or K or ^k: Turn 1 lines to the file header

Q: Exit

G: Back to File header

G: Turn to the tail of the file

Text Search:

/keyword:

Searches for the trailing end of the file from the current location with the string specified as keyword: case insensitive to characters

N: Next

N: Previous

? KEYWORD:

Contrary to/keyword usage

Exercise: Date command

What is the day of the week?

Set the current system time?

Show today's date, shape: 08/15/15?

Displays the current time, in the form of: 16:01:21?

(3) Info

Info COMMAND

(4) Help documentation for the program itself

/usr/share/doc/command-version

(5) Official program document

Official website

(6) Official documents of the release version

Http://www.redhat.com/docs

(7) Google

OpenStack Filetype:pdf #指定搜索的openstack文档为PDF格式

OpenStack site:openstack.com #指定在openstack. com site for Search

(8) SlideShare

https://www.slideshare.net/

1.2-linux command Help to get detailed