Shell programming notes, shell programming

Shell programming notes, shell programming
1. Bash variable
User-Defined variables # local variables
Environment Variable # global variable
Location Parameter Variable
Predefined Variables

X = val # value assignment
$ X # Call
The default value of the variable is quiet and cannot be calculated directly.
"$ X" $ {x} variable superposition, that is, string

Set # view all System Variables
-U: an error is reported if the variable does not exist.
Unset # Clear variable

Pstree # view the process tree

Export x # convert x into an environment variable

PATH = "$ PATH":/root

PS1 variable
\ D Display date "week Month day"
\ H displays the complete host name
\ T "HH: MM: SS"
\ A "HH: MM"
\ U current user name
\ W full name of the current directory
\ W the last directory of the current directory
\ $ Prompt

Language Variables
Echo $ LANG # current language environment
Locale-a | more # All Language Environments
/Etc/sysconfig/i18n # default language environment, which is enabled upon next boot

Location Parameter Variable
$ N is a number, $0 indicates the command itself, $1-$9 indicates the first to ninth parameters, more than 10 $ {10}
$ * Represents all the parameters in the command line, a whole
$ @ All parameters of the command line. Separate them.
$ # Number of command line parameters

Predefined Variables
$? The returned status of the Last Command executed. If it is 0, it is correct.
$ Pid of the current process
$! Pid of the last process running in the background

Read [Option] [variable name]
-P "prompt information": the output prompt information is waiting for input.
-T seconds: Specifies the waiting time.
-N characters: only the specified characters are allowed.
-S: input is not echo

2. Operators
Declare [+/-] [Option] variable name # variable type declaration
+ Cancelling variable type attributes
-Set type attributes
-A declares it as an array.
-I integer
-X Environment Variables
-R read-only # VARIABLES declared as read-only cannot be operated at all !!!
-P display type

Declare an array
Movie [0] = zp
Movie [1] = tp
Declare-a moive [2] = live
View Arrays
Echo $ {movie}
Echo $ {movie [2]}
Echo $ {movie [*]}

Export variable name <==> declare-x variable name

Declare-p # list all system variable types


Numeric operation
Expr let
Dd = $ (expr $ aa + $ bb)
$ (Expression ))
Ff = $ ($ aa + $ bb ))
$ [Expression]
Gg = $ [$ aa + $ bb]

Variable Test
# Used in script Optimization
# Visit www.imooc.com/video/6832

3. environment variable configuration file (loaded sequentially at startup)
Source configuration file #. Configuration File
/Etc/profile
/Etc/profile. d/*. sh
~ /. Bash_profile
~ /. Bashrc
/Etc/bashrc # defines PS1, that is, the logon prompt.

Umask # view the default system permissions ---- w -- w-
The Maximum File Permission is 666 # rw-
The directory has a maximum permission of 777 # rwxrwxrwx
The permission cannot be converted using numbers, but must contain letters.
Umask-defined permissions are the permissions to be discarded in the system's default permissions ~

Environment variable configuration file effective upon Cancellation
~ /. Bash_logout # logout Configuration
~ /. Bash_history # Save the history command. The current logon history command is stored in the memory.
#/Etc/profile HISTSIZE

Login file # only valid for local terminals
/Etc/issue # logon warning information
Escape characters that can be displayed
\ D current system date
\ S operating system name
\ L local terminal
\ M hardware architecture
\ N Host Name
\ O Domain Name
\ R kernel version
\ T current system time
\ U serial number of the current Login User

Remote Terminal welcome information # escape characters not supported
/Etc/issue.net # Add "Banner/etc/issue.net" to/etc/ssh/sshd_config to display (Restart sshd)

Information displayed after logon # supported by local remote connection
/Etc/motd


4. Condition judgment
File Type judgment, true
-Block B Devices
-C character device
-D directory
-E is true
-F: Common File
-L link file
-P MPs queue File
-S non-empty is true
-S socket File

Test-e/root/install. log
[-E/root/install. log]
[-D/root] & echo yes | echo no

File Permission judgment
-R read
-W write
-X execution
-U SUID
-G SGID
-K SBit

Compare two files
F1-nt f2 determine whether the f1 modification time is newer than f2
F1-ot f2 determines whether the f1 modification time is earlier than f2
F1-ef f2 determine whether Inode is consistent (determine hard link)

Two Integers
-Eq-ne-gt-lt-ge-le

String judgment
-Z string # True if it is null
-N string # non-null, true
String 1 = string 2 # equal to true
String 1! = String 2 # not equal to true

Condition Statement
If [conditional statement]; then
Program
Fi
# Or
If [condition 1]
Then
The condition is true, and the procedure 1
Elif [condition 2]
Then
The condition is not true, and the procedure 2
Else
Program
Fi

Case statement
Case $ variable name in
"Val1 ")
Part1
;;
"Val2 ")
Part2
;;
*)
Part default
;;
Esac

For Loop
For variable in val1 val2 val3...
Do
Program
Done

For (I = 1; I <100; I = I + 1 ))
Do
Program
Done

While & until Loop
While [conditional criterion]
Do
Program
Conditional increment # For example, I =$ ($ I + 1 ))
Done

The condition when until is equal to while

5. Regular Expression
Grep awk sed contains matching # Regular Expression
Ls find cp exact match # wildcard

* Any first character

Matching date
[0-9] \ {4 \}-[0-9] \ {2 \}-[0-9] \ {2 \}
Matching ip Address
[0-9] \ {1, 3 \}\. [0-9] \ {1, 3 \}\. [0-9] \ {1, 3 \}\. [0-9] \ {1, 3 \}

Cut [Option] file name # field Extraction
-F Field
-D separator # default Tab

Printf'output type output format' output content
% Ns output several characters
% Ni
% M. Number of floating points of nf

Awk 'condition 1 {Action 1} condition 2 {Action 2}... 'file name # Complex
# Df-h | grep "/dev/sda2" | awk '{print $5}' | cut-d "%"-f 1
# Awk 'in in {print "..."}{...}'
FS specified delimiter
# Cat/etc/passwd | grep/bin/bash | awk 'in in {FS = ":"} {print $1 "\ t" $3 }'
# Cat student.txt | grep-v Name | awk '$4> = 70 {print $2 }'

Sed [Option] '[action]' file name
# Action
-A append
-Replace row c
-Insert before I row
-P print
-S
-D. delete a row.

Character Processing
Sort [Option] File Name
-F case-insensitive
-N is sorted in numerical order.
-R reverse sorting
-T specifies the delimiter
-K n [, m]: sort by specified field. Start with n and end with m.

Wc [Option] File Name
-L line
-W words
-M characters

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