Linux Shell Programming Commands-linux Basic Environment Command Learning notes

1. Regular expressions

1) ^ Start * Previous character repeats more than 0 times

+ More than 1 times

? 0 or 1 times

. An arbitrary character (. *)

{m,n} m to n times

[0-9] [A-z] any number or letter

$ end Character

2) sed and awk commands

Sed ' match condition/executed action '/etc/passwd sed ' s/old/new/g '

Awk-f: ' {print '} '/etc/passwd 1 represents the first column, and 2 indicates the second column-F: The delimiter is:

2. Variables

1) environment variable system environment variable (/etc/profile) User environment variable (/home/user name/.bash_profile)

Set view

2) Position Variable $0-9

$ A script name

$1-9 Positional parameters

3) pre-defined variables

$! PID number of the last process running in the background

$? Program exit representatives (0 successes)

$* the contents of all parameters

$$ ID number of the current process

$# the number of arguments for the current shell

[email protected] All parameter contents (read one by one)

4) Custom Variables

Name=[value] PS: No spaces on either side of the equals sign, variable names are size sensitive

$ Variable Name value

3. Arithmetic operations

+ - * / %

$ ((expression))

$[-expression]

Expr expression expr 5 + 2 with spaces between variables

4. Built-in test judgment

Test-tested expression

[Test expression] PS: There must be a space between the test expression and []

Numerical comparison

-lt less than Ex:test &a-lt &b echo $?

-GT Greater than

-eq equals

-ne Not equal to

-le less than or equal to

-ge greater than or equal to

String test

= equals

！ = Not equal to

-Z String string length pseudo (0) True

The-n string length is not pseudo-true

File test

-e filename File exists then true

-r filename File exists and is readable as true

-W File name writable

-X File name executable

-S has at least one character in the filename file

-d filename file exists and is directory

-f filename File exists and is normal file

! (non) >>-a (with) >>-o (or)

5. Logical compliance between commands

&& Logic and

CMD1 && cmd2 cmd1 Execution succeeds CMD2

|| Logical OR

cmd1 | | CMD2 Cmd1 failed to execute CMD2

; no logical relationship

6. Common commands

Date-s "2016-04-12 15:20:13" to modify the system time

Date ' +y%m%d ' output system time according to date format

date-d ' 7 day ago ' +y%m%d ' output 7 days ago

7. Take a string

${variable name: Offset:length} Echo ${a%.*}

8. Writing code

#!/bin/bash declaring a running environment

How to run a. Granting permissions to run directly

B. Run bash 1.sh sh 1.sh by running environment

C.. 1.sh Source 1.sh

9. Control statements

1) For statement

A. For variable in value 1 value 2 ... Value n Variable value 1 ... Value n

Do

Command set {1..50} ' SEQ 50 ' takes value from 1 to 50

Done

B. for (initialize variable; end loop condition; variable operation))

2) While loop

A. While [condition] let i=i+1---i=$[i+1] I self-increment 1

B. While Read-r line

Do

Echo $line

Done </etc/passwd reads lines from the path and assigns values to line

3) If statement

If condition

Then

Command sequence

Elif conditions

Then

Command sequence

Else

Command sequence

Fi

4) Case statement

A. Case $ variable name in

Condition 1)

Command sequence

；；

Condition 2)

Command sequence

；；

*) above are not satisfied

Esac

10. Functions

A. Name () {

Command sequence

}

B. function name{

Command sequence

}

11. Scheduled Tasks

1) One-time scheduled tasks

At time Ctrl+d end input

At-l List Current Scheduled tasks

2) Recurring Scheduled task Service Crond start (Status,restart)

A. Boot from boot

Chkconfig--list lists whether system services are powered on from boot (3 and 5)

B. Developing the content of the planned tasks

CRONTAB-E (Enter) >> Enter VI command

Time and Command day and Night Week (no * substitution-Indicates continuous time, indicating a number of discontinuous time/interval time) cmd command */10 * * * * ntpdate time server IP synchronizes clocks every 10 minutes

C. Restart Service Crond Restart

Linux Shell Programming Commands-linux Basic Environment Command Learning notes