Introduction to basic commands under Linux (i)

I. BASIC commands

1. Type Command----View the types of commands

A. built-in commands (internal command) shell built-in

B. external Command ----An executable file with a command name in a path on the file system

Usage:type command name

Judging by the value returned, if the value is a shell builtin then it is a built-in command, if it is not the value but a path then it is an external command

2.printenv Command---View environment variables

echo $PATH ----The value of the output environment variable, using a colon-delimited path

3.Set command--View all system variables

4.echo command-The value of the output variable

Usage:echo $ variable name

Assign a value to a variable without the $ character direct variable name = "Variable Value"

Question: How to output two variables in one command and let them show in two lines

echo-e "$HOSTNAME \ n $USER"

To use the escape character \ n requires the-e option

Issue: Echo command defaults to output after wrapping how to output without wrap

echo-n $name

5.Clear Command---clear screen (same as crtl+l function)

6.date or Clock command---View the current system time

Usage: Date +%d Formatted output requires a character + in front of the format character +

Date + "This is%Y"

Issue: Output line break

Date + "This year was Y%n today is%d"

7.hwclock Command---View hardware time

Hwclock-s synchronizing the hardware clock to the system clock

Hwclock-w synchronizing the system clock to the hardware clock

8. Man Command---Get external command Help (manual user manual)

You can also use: command name--help to get External command brief usage information

Usage: Man 2 command

2 represents the number of chapters to view

Manual commands are displayed in sub-chapters

A. Chapter I user commands (available to/bin,/usr/bin,/usr/local/bin administrators and ordinary users)

B. Chapter II system invocation

C. Third-chapter library invocation

D. Chapter IV Special documents (character device files, block device files)

E. Chapter V file format (the syntax of the configuration file, which represents the interpretation of the meaning of each field in the file)

F. sixth chapter game

G. seventh Chapter Miscellaneous

H. eighth chapter Management commands (/sbin,/usr/sbin,/usr/local/sbin only available to administrators)

<>: Required

[]: Optional

... : multiple times can occur

|: Choose one More

{}: Grouping

Mans:

Name: command names and features brief description

Synopsis: Usage notes, including available options

DESCRIPTION: A detailed description of the command function, which may include the meaning of each option

Options: Explaining the meaning of each option

Files: The configuration file associated with this command

BUGS:

EXAMPLES: Using the example

See ALSO: Another reference

Flip Screen:

Turn back one screen: SPACE

Turn One screen forward: b

Turn back one line: ENTER

Turn One line forward: K

Find:

/keyword: Backwards

N: Next

N: Previous

? KEYWORD: Forward

N: Next

N: Previous

Q: Exit

9. help command---Get assistance with internal commands

whatis Command---View the command is in the section of the Manual manual.

Usage: Whatis command

11. Documentation:/usr/share/doc

Thecal command---Display the calendar table

The argument can be a certain year of the month

13. Question:

A.echo is an internal or external command

Type echo---internal command

The role of the B.man command

Man echo function to show help for the echo command

C. How to use echo to wrap a line display

Echo-e "$HOSTNAME \n$path"

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Introduction to basic commands under Linux (i)